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Fluctuations in platelet count levels over time may help distinguish immune thrombocytopenia (ITP) from other causes of thrombocytopenia. We derived the platelet variability index (PVI) to capture both the fluctuations in platelet count measurements and the severity of the thrombocytopenia over time. Raw PVI values, ranging from negative (less severe thrombocytopenia and/or low fluctuations) to positive (more severe thrombocytopenia and/or high fluctuations) were converted to an ordinal PVI score, from 0 to 6. We evaluated the performance characteristics of the PVI score for consecutive adults with thrombocytopenia from the McMaster ITP Registry. We defined patients with definite ITP as those who achieved a platelet count response after treatment with intravenous immune globulin or high-dose corticosteroids and possible ITP as those who never received ITP treatment or did not respond to treatment. Of 841 patients with thrombocytopenia, 104 had definite ITP, 398 had possible ITP, and 339 had non-ITP thrombocytopenia. For patients with definite ITP, the median PVI score was 5 [interquartile range (IQR) 5, 6] for patients with possible ITP, the median PVI score was 3 (1, 5); and for patients with non-ITP thrombocytopenia, the median PVI score was 0 (0, 2). A high PVI score correlated with the diagnosis of definite ITP even when calculated at the patient’s initial assessment, before any treatment had been administered. Platelet count fluctuations alone contributed to the specificity of the overall PVI score. The PVI score may help clinicians diagnose ITP among patients who present with thrombocytopenia for evaluation.

Background Immune thrombocytopenia (ITP) is an autoimmune disease characterized by low platelet counts and increased risk of bleeding. In preparation for an upcoming guideline, the ITP Emergency Management Guideline Panel, including clinical experts in hematology, emergency medicine, research methodology, and patient representatives, identified the need for a standardized definition of a critical ITP bleed. The goal of the definition was to distinguish critical bleeds from bleeds that may not require urgent treatment, typically in the context of severe thrombocytopenia. Methods The panel met in person and virtually to achieve consensus on the criteria for critical bleeding events among patients with ITP. Existing ITP bleeding scores and published definitions of major bleeds in patients receiving anticoagulation informed the definition of a critical ITP bleed. The Platelet Immunology Scientific Standardization Committee (SSC) of the International Society on Thrombosis and Haemostasis endorsed the definition. Results A critical ITP bleed was defined as: (a) a bleed in a critical anatomical site including intracranial, intraspinal, intraocular, retroperitoneal, pericardial, or intramuscular with compartment syndrome; or (2) an ongoing bleed that results in hemodynamic instability or respiratory compromise. Conclusion The definition of a critical ITP bleed was developed by the ITP Emergency Management Guideline Panel and endorsed by the Platelet Immunology SSC. It incorporates both anatomic and physiologic risk and pertains to patients with confirmed or suspected ITP who typically have severe thrombocytopenia (platelet count below 20 × 109 /L).

Vaccine-induced immune thrombotic thrombocytopaenia (VITT) is a rare adverse effect of COVID-19 adenoviral vector vaccines1–3. VITT resembles heparin-induced thrombocytopaenia (HIT) in that it is associated with platelet-activating antibodies against platelet factor 4 (PF4)4; however, patients with VITT develop thrombocytopaenia and thrombosis without exposure to heparin. Here we sought to determine the binding site on PF4 of antibodies from patients with VITT. Using alanine-scanning mutagenesis5, we found that the binding of anti-PF4 antibodies from patients with VITT (n = 5) was restricted to eight surface amino acids on PF4, all of which were located within the heparin-binding site, and that the binding was inhibited by heparin. By contrast, antibodies from patients with HIT (n = 10) bound to amino acids that corresponded to two different sites on PF4. Biolayer interferometry experiments also revealed that VITT anti-PF4 antibodies had a stronger binding response to PF4 and PF4–heparin complexes than did HIT anti-PF4 antibodies, albeit with similar dissociation rates. Our data indicate that VITT antibodies can mimic the effect of heparin by binding to a similar site on PF4; this allows PF4 tetramers to cluster and form immune complexes, which in turn causes Fcγ receptor IIa (FcγRIIa; also known as CD32a)-dependent platelet activation. These results provide an explanation for VITT-antibody-induced platelet activation that could contribute to thrombosis. Alanine-scanning mutagenesis is used to identify the PF4 epitope that is recognized by anti-PF4 antibodies in patients with vaccine-induced immune thrombotic thrombocytopaenia, revealing that the epitope corresponds to the heparin-binding site on PF4.

Misclassification of immune thrombocytopenia (ITP) is common, which might undermine the value of platelet autoantibody testing. We determined the sensitivity and specificity of platelet autoantibody testing using the direct antigen capture assay for anti-glycoprotein (GP) IIb/IIIa or anti-GPIbIX in patients with 'definite ITP', defined as those with a documented treatment response. Sensitivity of platelet autoantiboody testing increased from 48·3% [95% confidence interval (CI) 43·5-53·2] for all ITP patients to 64·7% (95% CI 54·6-73·9) for definite ITP patients. Specificity was unchanged [75·3% (95% CI 67·5-82·1)]. High optical density values (>0·8) improved the specificity of platelet autoantibody testing but lowered sensitivity. In patients with a high pretest probability, platelet autoantibodies can aid in the diagnosis of ITP and may be most prevalent in certain patient subsets.

Background Functional platelet activation assays, such as the serotonin release assay (SRA), are the gold standard for the diagnosis of heparin-induced thrombocytopenia (HIT). Recently, platelet activation assays using added platelet factor 4 (PF4) have been described and suggest improved sensitivity. Direct comparisons of these assays have not been performed. Objective We compare the performance characteristics of three PF4-enhanced platelet activation assays, the PF4/heparin-SRA (PF4/hep-SRA), the PF4-SRA, and the P-selectin expression assay (PEA), at a single reference laboratory. Methods Serum samples from two cohorts of patients were used. The referral cohort (n = 84) included samples that had previously undergone routine diagnostic testing for HIT and tested positive or negative using the SRA. The clinical cohort (n = 101) consisted of samples from patients with clinically confirmed HIT whose serum contained platelet-activating antibodies. We simultaneously tested all samples in PF4-enhanced SRA-based assays (PF4/hep-SRA, PF4-SRA) and the flow cytometry-based PEA. Results In the referral cohort, the three PF4-enhanced assays identified all samples that were previously determined to be positive in the SRA. However, specificity of the PF4/hep-SRA was 96.6%, the PF4-SRA was 84.7%, and the PEA was 67.8%. In the clinical cohort of samples, all SRA-based assays displayed high performance characteristics (>92.1% sensitivity, >98.4% specificity). Sensitivity and specificity of the PEA was the lowest, 65.8% and 63.5%, respectively; but improved to 92.1% and 96.8% using preselected platelet donors. Conclusions All PF4-enhanced assays demonstrated good performance characteristics when platelet donors were preselected. Further comparisons across multiple laboratories should be conducted for consensus on optimal HIT diagnostic testing.

Fetal and neonatal alloimmune thrombocytopenia (FNAIT) is the most common cause of intracranial hemorrhage (ICH) in thrombocytopenic term infants. We investigated clinical and laboratory predictors of severe FNAIT in a tertiary care referral center.Retrospective cohort study over a 30-year period. We defined FNAIT as recurrence of neonatal thrombocytopenia in a subsequent pregnancy; and severe outcomes as any of: (1) a birth platelet count below 20 × 10During index pregnancies (n = 135 in 131 mothers), 71 infants (52.6%) had severe outcomes including a platelet count20 × 10The presence of anti-HPA is highly indicative of the diagnosis of severe FNAIT; however, we observed one infant who had severe FNAIT recurrence, defined using strict clinical criteria, without a maternal antibody. Improved diagnostic and therapeutic strategies are needed to prevent severe FNAIT in high-risk mothers.

Adenoviral vector vaccines are effective against SARS-CoV-2 but have been associated with a rare side effect termed vaccine-induced immune thrombotic thrombocytopenia (VITT). Here, we discuss our understanding of how vaccine-induced antibodies to platelet factor 4 (PF4) form immune complexes that activate platelets and trigger the thrombotic events seen in VITT., Here, John Kelton and colleagues provide an overview of vaccine-induced immune thrombotic thrombocytopenia (VITT), a very rare complication that has been observed following vaccination with adenoviral vector-based COVID-19 vaccines.

Immune complexes assemble on the platelet surface and cause Fc-mediated platelet activation in heparin-induced thrombocytopenia (HIT); however, it is not known if fluid-phase immune complexes contribute to HIT. The objective of this study was to understand the role of fluid-phase immune complexes in platelet activation and HIT. Binding of wild-type and 15 platelet factor 4 (PF4) mutants to platelets was measured using flow cytometry. Platelet activation was measured using the PF4-dependent 14C-serotonin release assay (PF4-SRA) with KKO and a HIT-patient plasma in the presence of wild-type or PF4 mutants. To activate platelets, we found that a minimal level of wild-type PF4 is required to bind the platelet surface in the presence of KKO (2.67 relative MFI) or HIT-patient plasma (1.71 relative MFI). Only a subset of PF4 mutants was able to support platelet activation, despite having lower surface binding than the minimum binding required of wild-type PF4 (9 mutants with KKO and 2 mutants with HIT-patient plasma). Using individual PF4 mutants, we identified that HIT immune complexes can be formed in fluid-phase and induce platelet activation. Further studies are required to investigate the role of fluid-phase HIT immune complexes in the development of thrombocytopenia and thrombosis associated with clinical HIT.

Background: Patients with immune thrombocytopenia are at risk of bleeding during surgery, and intravenous immunoglobulin is commonly used to increase the platelet count. We aimed to establish whether perioperative eltrombopag was non-inferior to intravenous immunoglobulin. Methods: We did a randomised, open-label trial in eight academic hospitals in Canada. Patients were aged at least 18 years, with primary or secondary immune thrombocytopenia and platelet counts less than 100 × 109 cells per L before major surgery or less than 50 × 109 cells per L before minor surgery. Previous intravenous immunoglobulin within 2 weeks or thrombopoietin receptor agonists within 4 weeks before randomisation were not permitted. Patients were randomly assigned to receive oral daily eltrombopag 50 mg from 21 days preoperatively to postoperative day 7 or intravenous immunoglobulin 1 g/kg or 2 g/kg 7 days before surgery. Eltrombopag dose adjustments were allowed weekly based on platelet counts. The randomisation sequence was generated by a computerised random number generator, concealed and stratified by centre and surgery type (major or minor). The central study statistician was masked to treatment allocation. The primary outcome was achievement of perioperative platelet count targets (90 × 109 cells per L before major surgery or 45 × 109 cells per L before minor surgery) without rescue treatment. We did intention-to-treat and per-protocol analyses using an absolute non-inferiority margin of –10%. This trial is registered with ClinicalTrials.gov, NCT01621204. Findings: Between June 5, 2013, and March 7, 2019, 92 patients with immune thrombocytopenia were screened, of whom 74 (80%) were randomly assigned: 38 to eltrombopag and 36 to intravenous immunoglobulin. Median follow-up was 50 days (IQR 49–55). By intention-to-treat analysis, perioperative platelet targets were achieved for 30 (79%) of 38 patients assigned to eltrombopag and 22 (61%) of 36 patients assigned to intravenous immunoglobulin (absolute risk difference 17·8%, one-sided lower limit of the 95% CI 0·4%; pnon-inferiority=0·005). In the per-protocol analysis, perioperative platelet targets were achieved for 29 (78%) of 37 patients in the eltrombopag group and 20 (63%) of 32 in the intravenous immunoglobulin group (absolute risk difference 15·9%, one-sided lower limit of the 95% CI –2·1%; pnon-inferiority=0·009). Two serious adverse events occurred in the eltrombopag group: one treatment-related pulmonary embolism and one vertigo. Five serious adverse events occurred in the intravenous immunoglobulin group (atrial fibrillation, pancreatitis, vulvar pain, chest tube malfunction and conversion to open splenectomy); all were related to complications of surgery. No treatment-related deaths occurred. Interpretation: Eltrombopag is an effective alternative to intravenous immunoglobulin for perioperative treatment of immune thrombocytopenia. However, treatment with eltrombopag might increase risk of thrombosis. The decision to choose one treatment over the other will depend on patient preference, resource limitations, cost, and individual risk profiles. Funding: GlaxoSmithKline and Novartis.

Autoantibodies cause platelet destruction in patients with immune thrombocytopenia (ITP); yet only 50% to 60% of patients have detectable platelet autoantibodies in peripheral blood. We hypothesized that in some ITP patients, platelet autoantibodies are sequestered in the bone marrow where pathological immune reactions target megakaryocytes or newly formed platelets. In this study, we modified the platelet glycoprotein-specific assay to test bone marrow aspiration samples for free platelet autoantibodies or antibodies bound to bone marrow cells in aspirate fluid from patients with ITP (n = 18), patients with nonimmune thrombocytopenia (n = 3), and healthy donors (n = 6). We found that 10 (56%) of 18 patients with ITP had autoantibodies in the bone marrow, including 5 (50%) of 10 with autoantibodies in bone marrow only, and 5 (50%) of 10 with autoantibodies in bone marrow and peripheral blood. In comparison, 6 (33%) of 18 ITP patients had autoantibodies in peripheral blood, most of whom (5 [83%] of 6) also had autoantibodies in bone marrow. Bone marrow autoantibodies were not detected in patients with nonimmune thrombocytopenia or healthy donors; however, peripheral blood autoantibodies were detectable in 1 (33%) of 3 patients with nonimmune thrombocytopenia. The sensitivity of platelet autoantibodies for the diagnosis of ITP increased from 60% (peripheral blood testing) to 72% (peripheral blood and bone marrow testing). Immune reactions limited to the bone marrow may be characteristic of certain subsets of ITP patients.

Vaccine-induced immune thrombotic thrombocytopenia (VITT) is a rare but serious adverse syndrome occurring 5 to 30 days after adenoviral vector COVID-19 vaccination. Therefore, a practical evaluation of clinical assessments and laboratory testing for VITT is needed to prevent significant adverse outcomes as the global use of adenoviral vector vaccines continues. We received the clinical information and blood samples of 156 patients in Canada with a suspected diagnosis of VITT between April and July 2021. The performance characteristics of various diagnostic laboratory tests were evaluated against the platelet factor 4 (PF4)-14C-serotonin release assay (SRA) including a commercial anti-PF4/heparin immunoglobulin G (IgG)/IgA/IgM enzyme immunoassay (EIA, PF4 Enhanced; Immucor), in-house IgG-specific anti-PF4 and anti-PF4/heparin-EIAs, the standard SRA, and the PF4/heparin-SRA. Of those, 43 (27.6%) had serologically confirmed VITT-positive based on a positive PF4-SRA result and 113 (72.4%) were VITT-negative. The commercial anti-PF4/heparin EIA, the in-house anti-PF4-EIA, and anti-PF4/heparin-EIA were positive for all 43 VITT-confirmed samples (100% sensitivity) with a few false-positive results (mean specificity, 95.6%). These immunoassays had specificities of 95.6% (95% confidence interval [CI], 90.0-98.6), 96.5% (95% CI, 91.2-99.0), and 97.4% (95% CI, 92.4-99.5), respectively. Functional tests, including the standard SRA and PF4/heparin-SRA, had high specificities (100%), but poor sensitivities for VITT (16.7% [95% CI, 7.0-31.4]; and 46.2% [95% CI, 26.6-66.6], respectively). These findings suggest EIA assays that can directly detect antibodies to PF4 or PF4/heparin have excellent performance characteristics and may be useful as a diagnostic test if the F4-SRA is unavailable.

The association between T-cell large granular lymphocytes (T-LGL) and ITP is uncertain. The aims of this study were to determine the prevalence of T-LGL in patients with ITP and to describe its association with ITP disease severity. We analyzed flow cytometry results for T-LGL (using a threshold of 0.3 x109 or greater cells/L) or positive T-cell receptor clonality in patients with ITP and nonimmune thrombocytopenia. Descriptive statistics were used to characterize the association between T-LGL and ITP, response to ITP treatments (rituximab and splenectomy) and response to T-LGL treatment. Among ITP patients, 14.3% (13/91) had evidence of a T-LGL population compared to 10.3% (3/29) of patients with non-immune thrombocytopenia. ITP patients with T-LGL had lower nadir platelet counts (2 vs. 47 × 109/L) and received more ITP treatments (median 6 vs. 3) than ITP patients without T-LGL. Response to rituximab was observed in 14.3% (1/7) of ITP patients with T-LGL and 54.5% (6/11) without T-LGL. Response to splenectomy was observed in 25% (2/8) with T-LGL and 56.2% (9/16) without T-LGL. Four patients with ITP and T-LGL received treatment for T-LGL with methotrexate; none had an improvement in platelet count levels. T-LGL may appear in patients with ITP, and the meaning of this finding remains unclear; however, for some patients, the presence of abnormal T-LGL may indicate a more severe form of ITP that tends to be less responsive to therapy. In this cohort, treatment of T-LGL with methotrexate did not improve platelet counts in the few patients who were treated.

Coronavirus Disease 2019 (COVID-19) is a global pandemic caused by the novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). While detection of SARS-CoV-2 by polymerase chain reaction with reverse transcription (RT-PCR) is currently used to diagnose acute COVID-19 infection, serological assays are needed to study the humoral immune response to SARS-CoV-2. Anti-SARS-CoV-2 immunoglobulin (Ig)G/A/M antibodies against spike (S) protein and its receptor-binding domain (RBD) were characterized in recovered subjects who were RT-PCR-positive (n = 153) and RT-PCR-negative (n = 55) using an enzyme-linked immunosorbent assay (ELISA). These antibodies were also further assessed for their ability to neutralize live SARS-CoV-2 virus. Anti-SARS-CoV-2 antibodies were detected in 90.9% of resolved subjects up to 180 days post-symptom onset. Anti-S protein and anti-RBD IgG titers correlated (r= 0.5157 and r= 0.6010, respectively) with viral neutralization. Of the RT-PCR-positive subjects, 22 (14.3%) did not have anti-SARS-CoV-2 antibodies, and of those, 17 had RT-PCR cycle threshold (Ct) values &gt, 27. These high Ct values raise the possibility that these indeterminate results are from individuals who were not infected or had mild infection that failed to elicit an antibody response. This study highlights the importance of serological surveys to determine population-level immunity based on infection numbers as determined by RT-PCR.

Background Thrombocytopenia and thrombosis are prominent in coronavirus disease 2019 (COVID-19), particularly among critically ill patients; however, the mechanism is unclear. Such critically ill COVID-19 patients may be suspected of heparin-induced thrombocytopenia (HIT), given similar clinical features. Objectives We investigated the presence of platelet-activating anti-platelet-factor 4 (PF4)/heparin antibodies in critically ill COVID-19 patients suspected of HIT. Patients/methods We tested 10 critically ill COVID-19 patients suspected of HIT for anti-PF4/heparin antibodies and functional platelet activation in the serotonin release assay (SRA). Anti-human CD32 antibody (IV.3) was added to the SRA to confirm FcγRIIA involvement. Additionally, SARS-CoV-2 antibodies were measured using an in-house ELISA. Finally, von Willebrand factor (VWF) antigen and activity were measured along with A Disintegrin And Metalloprotease with ThromboSpondin-13 Domain (ADAMTS13) activity and the presence of anti-ADAMTS13 antibodies. Results Heparin-induced thrombocytopenia was excluded in all samples based on anti-PF4/heparin antibody and SRA results. Notably, six COVID-19 patients demonstrated platelet activation by the SRA that was inhibited by FcγRIIA receptor blockade, confirming an immune complex (IC)-mediated reaction. Platelet activation was independent of heparin but inhibited by both therapeutic and high dose heparin. All six samples were positive for antibodies targeting the receptor binding domain (RBD) or the spike protein of the SARS-CoV-2 virus. These samples also featured significantly increased VWF antigen and activity, which was not statistically different from the four COVID-19 samples without platelet activation. ADAMTS13 activity was not severely reduced, and ADAMTS13 inhibitors were not present, thus ruling out a primary thrombotic microangiopathy. Conclusions Our study identifies platelet-activating ICs as a novel mechanism that contributes to critically ill COVID-19.

Thrombosis is a prominent feature of coronavirus disease 2019 (COVID-19) and often occurs in patients who are critically ill; however, the mechanism is unclear. This COVID-19 associated coagulopathy (CAC) shares features with heparin-induced thrombocytopenia (HIT), including mild thrombocytopenia and thrombosis. We thus tested 10 CAC patients for anti-PF4/heparin antibodies and functional platelet activation. HIT was excluded in all samples based on anti-PF4/heparin antibody and serotonin release assay results. Of note, 6 CAC patients demonstrated platelet activation by the serotonin release assay that was inhibited by FcγRIIA receptor blockade, confirming an IgG-specific immune complex (IC)-mediated reaction. Platelet activation was independent of heparin, but inhibitable by both therapeutic and high dose heparin. All 6 samples were positive for IgG-specific antibodies targeting the receptor binding domain (RBD) or the spike protein of the SARS-CoV-2 virus. These samples were additionally characterized by significant endothelial activation, shown by increased von Willebrand factor antigen and activity. ADAMTS13 activity was not severely reduced, and ADAMTS13 inhibitors were not present, ruling out thrombotic thrombocytopenic purpura. Our study thus identifies platelet-activating ICs as a mechanism that contributes to CAC thrombosis.Scientific CategoryThrombosis and HemostasisKey PointsPatients with COVID-19 thrombosis have immune complexes that activate platelets through FcγRIIA signallingPatients with COVID-19 thrombosis demonstrate increased VWF antigen and activity that is not related to severe ADAMTS13 reduction

Coronavirus Disease 2019 (COVID-19) is a global pandemic caused by the novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). While detection of SARS-CoV-2 by polymerase chain reaction with reverse transcription (RT-PCR) is currently used to diagnose acute COVID-19 infection, serological assays are needed to study the humoral immune response to SARS-CoV-2. SARS-CoV-2 IgG/A/M antibodies against SARS-CoV-2 spike (S) protein and its receptor-binding domain (RBD) were characterized using an enzyme-linked immunosorbent assay (ELISA) and assessed for their ability to neutralize live SARS-CoV-2 virus in recovered subjects who were RT-PCR-positive (n=153), RT-PCR-negative (n=55), and control samples collected pre-COVID-19 (n=520). Anti-SARS-CoV-2 antibodies were detected in 90.9% of resolved subjects up to 180 days post-symptom onset. Anti-S protein and anti-RBD IgG titers correlated (r= 0.5157 and r = 0.6010, respectively) with viral neutralization. Of the RT-PCR-positive subjects, 22 (14.3%) did not have anti-SARS-CoV-2 antibodies; and of those, 17 had RT-PCR cycle threshold (Ct) values >27, raising the possibility that these indeterminate results are from individuals who were not infected, or had mild infection that failed to elicit an antibody response. This study highlights the importance of serological surveys to determine population-level immunity based on infection numbers as determined by RT-PCR.

In this report, we will review the various clinical and laboratory approaches to diagnosing immune thrombocytopenia (ITP), with a focus on its laboratory diagnosis. We will also summarize the results from a number of laboratories that have applied techniques to detect anti-platelet autoantibodies as diagnostic tests for ITP. Although there is considerable variability in methods among laboratories, there is general agreement that platelet autoantibody testing has a high specificity but low sensitivity. This suggests several possibilities: (1) the ideal test for ITP has yet to be developed, (2) current test methods need to be improved, or (3) ITP is the clinical expression of a variety of thrombocytopenic disorders with different underlying mechanisms. Even the clinical diagnosis of ITP is complex, and experienced clinicians do not always agree on whether a particular patient has ITP. Improvements in the diagnostic approach to ITP are necessary to improve the management of this disorder.

Summary Rituximab is an effective therapy resulting in a platelet count improvement in 60% of patients with immune thrombocytopenia (ITP). Rituximab depletes B cells; thus, a reduction in platelet autoantibody levels would be anticipated in patients who achieve a clinical response to this treatment. The objectives of this study were to determine whether rituximab was associated with a reduction in platelet autoantibody levels, and to correlate the loss of autoantibodies with the achievement of a treatment response. We performed a case-control study nested within a previous randomized controlled trial of standard therapy plus adjuvant rituximab or placebo. We measured platelet-bound anti-glycoprotein (GP) IIbIIIa and anti-GPIbIX using the antigen capture test. Of 55 evaluable patients, 25 (45%) had a detectable platelet autoantibody at baseline. Rituximab was associated with a significant reduction in anti-GPIIbIIIa levels (P = 0·02) but not anti-GPIbIX levels (P = 0·51) compared with placebo. Neither the presence of an autoantibody at baseline nor the loss of the autoantibody after treatment was associated with a response to rituximab. The subset of patients with persistent autoantibodies after treatment failed to achieve a platelet count response, suggesting that persistence of platelet autoantibodies can be a marker of disease severity.

Background: Patients with immune thrombocytopenia (ITP) are at risk of bleeding during surgery. Intravenous immune globulin (IVIG) is a blood product that is commonly used to increase platelet counts before surgery or invasive procedures for patients with ITP; however, eltrombopag, an oral thrombopoietin receptor agonist, may be an effective alternative. Methods: We conducted a multicenter randomised trial to determine whether eltrombopag was non-inferior to IVIG for the achievement of perioperative platelet count targets without the use of rescue treatment. We did an intention to treat and per-protocol analysis using an absolute non-inferiority margin of -10%. Secondary endpoints were thrombosis, bleeding, adverse events and treatment satisfaction. We enrolled 74 patients with ITP who had a planned major or minor surgery and with a platelet count below 100 x109/L or 50 x109/L respectively. Patients were randomised to receive oral daily eltrombopag from 21 days preoperatively, or IVIG (1 or 2g per kg) seven days preoperatively. Findings: By intention to treat, perioperative platelet targets were achieved by 30 of 38 patients (78·9%) assigned to eltrombopag and 22 of 36 patients (61·1%) assigned to IVIG (absolute difference, 17·8%; one-sided lower limit of the 95% confidence interval, 0·4%; p=0·005 for non-inferiority). Results were similar for patients who completed the protocol. One patient in the eltrombopag group developed a pulmonary embolism 14 days after minor surgery, and one patient in the IVIG group developed a distal deep vein thrombosis 30 days after major surgery. There was no difference in bleeding or adverse events. Patients reported higher treatment satisfaction with eltrombopag. Interpretation: Eltrombopag was no worse than IVIG for the achievement of platelet count targets around the time of surgery for patients with ITP. This population may be at increased risk of thrombosis. Trial Registration: www.clinicaltrials.gov number as NCT01621204. Funding Statement: This trial was funded by GlaxoSmithKline and Novartis. Declaration of Interests: N.M.H., R.J.C., M.B., J.K., A.T., M.S., M.W., P.V., J.C., N.L., S.L., and J.G.K. report no competing financial interests. D.M.A. reports grants from GlaxoSmithKline and Novartis during the conduct of the study; grants and/or personal fees from Novartis, Amgen, Bristol Myers Squibb, UCB, Principia, and Rigel outside the submitted work. C.H. reports personal fees from Novartis, Amgen, and GSK, outside the submitted work. E.J. reports personal fees from Novartis, outside the submitted work. M.S. reports personal fees from Novartis, outside the submitted work. Y.L. reports grants from Novartis during the conduct of the study, and other fees from Pfizer, outside the submitted work. L.L. reports personal fees from Novartis during the conduct of the study. S.A. reports grants from Novartis NL during the conduct of the study; grants from Amgen, outside the submitted work. W.L. reports personal fees from Novartis, outside the submitted work. Ethics Approval Statement: The trial was approved by the research ethics boards at each participating center. The study was conducted in accordance with the Declaration of Helsinki and Good Clinical Practice guidelines.

TO THE EDITOR: The management of anticoagulation in patients with immune thrombocytopenia (ITP) is challenging. This difficult clinical scenario is becoming increasingly common as the ITP population ages[1][1] and indications for anticoagulation broaden.[2][2] The clinical challenge stems from the

Heparin-induced thrombocytopenia (HIT) is a prothrombotic drug reaction caused by platelet-activating anti-platelet factor 4 (PF4)/heparin antibodies. Pathogenic HIT antibodies can be detected by the serotonin-release assay (SRA), a platelet activation test. We have regarded the SRA performed in our medical community ("McMaster" SRA) as having high sensitivity and specificity. Recently, the concept of "SRA-negative HIT" has been proposed for enzyme-immunoassay (EIA)-positive/SRA-negative patients with a HIT-compatible clinical picture, who test positive in a PF4-enhanced platelet activation assay. After identifying an index case of SRA-negative HIT, we estimated the frequency of this condition by performing the "PF4-SRA" (modified SRA using high concentrations of added PF4 rather than heparin) in EIA-positive patients from a cohort study evaluating clinical and laboratory diagnosis of HIT. We defined SRA-negative HIT as patients meeting three criteria: clinical picture compatible with HIT (4Ts ≥ 4 points); EIA-positive (≥1.00 units); and PF4-SRA-positive. Among 430 patients, 35 were EIA-positive/SRA-positive and 27 were EIA-positive/SRA-negative. Among these 27 SRA-negative patients, three were found to have subthreshold levels of platelet-activating antibodies by PF4-SRA, of whom one met clinical criteria for SRA-negative HIT. Thus, based on identifying one patient with SRA-negative HIT within a cohort study that found 35 SRA-positive HIT patients, we estimate the sensitivity of the McMaster SRA for diagnosis of HIT to be 35/36 (97.2%; 95% CI, 85.8-99.9%). Although the McMaster SRA is highly sensitive for HIT, occasional SRA-negative but EIA-positive patients strongly suspected of having HIT can have this diagnosis supported by a PF4-enhanced activation assay such as the PF4-SRA.

Background The Bridging ITP Trial is an open-label randomized trial designed to compare the oral thrombopoietin receptor agonist eltrombopag and intravenous immune globulin (IVIG) for patients with immune thrombocytopaenia (ITP) who require an increase in platelet count before elective surgery. Here, we report the study methods and rationale. Methods We designed a multi-centre, non-inferiority randomized trial comparing daily oral eltrombopag starting 3 weeks pre-operatively, and IVIG administered 1 week pre-operatively for patients with ITP requiring a platelet count increase prior to surgery. Starting dose of eltrombopag is 50 mg daily with a weekly pre-operative dose titration schedule, and treatment is continued for 1 week after surgical haemostasis is achieved. IVIG is administered at a dose of 1 to 2 g/kg 1 week pre-operatively with the allowance for a second dose within 1 week after surgical haemostasis. The objective of the study is to demonstrate non-inferiority of eltrombopag for the primary endpoint of achieving the pre-operative platelet count threshold (50 × 109/L for minor surgery; or 100 × 109/L for major surgery) and sustaining platelet count levels above the threshold for 1 week after surgical haemostasis is achieved, without the use of rescue treatment. Secondary endpoints include thrombosis, bleeding and patient satisfaction. Conclusion The Bridging ITP Trial will evaluate the efficacy and safety of eltrombopag as an alternative to IVIG in the peri-operative setting for patients with ITP. The protocol was designed to provide a management strategy that can be applied in clinical practice. ClinicalTrials.gov Identifier NCT01621204.

Essentials The diagnosis of ITP is based on a platelet count 90%). A positive autoantibody test can be useful to rule in ITP but a negative does not rule out ITP. SUMMARY: Background Immune thrombocytopenia (ITP) is an autoimmune disorder characterized by a low platelet count and an increased risk of bleeding. The sensitivity and specificity of platelet autoantibody tests is variable and their utility is uncertain. Objective The purpose of this study was to perform a systematic review and meta-analysis of platelet autoantibody tests in the diagnosis of ITP. Methods Ovid Medline, PubMed, and Web of Science were searched from inception until 31 May 2018. Two reviewers independently assessed studies for eligibility and extracted data. Studies that reported testing results for antiplatelet autoantibodies on platelets (direct tests) or in plasma/serum (indirect tests) for 20 or more ITP patients were included. Results Pooled estimates for sensitivity and specificity were calculated using a random effects model. Pooled estimates for the sensitivity and specificity of direct anti-platelet autoantibody testing for either anti-glycoprotein IIbIIIa or anti-glycoprotein IbIX were 53% (95% confidence interval [CI], 44-61%) and 93% (95% CI, 81-99%), respectively. For indirect testing, the pooled estimates for the sensitivity and specificity were 18% (95% CI, 12-24%) and 96% (95% CI, 87-100%), respectively. Conclusions Autoantibody testing in ITP patients has a high specificity but low sensitivity. A positive autoantibody test can be useful for ruling in ITP, but a negative test does not rule out ITP.

Essentials Many patients produce antibodies but few lead to heparin-induced thrombocytopenia (HIT). Pathogenic epitopes are difficult to identify as HIT antibodies are polyclonal and polyspecific. KKO binding to platelet factor 4 (PF4) depends on 13 amino acids, three of which are newly observed. Five amino acids in PF4 can help distinguish pathogenic from non-pathogenic antibodies. SUMMARY: Background Heparin-induced thrombocytopenia (HIT) is an adverse drug reaction that results in thrombocytopenia and, in some patients, thrombotic complications. HIT is mediated by antibodies that bind to complexes of platelet factor 4 (PF4) and heparin. The antigenic epitopes of these anti-PF4/heparin antibodies have not yet been precisely defined, because of the polyspecific immune response that characterizes HIT. Objectives To identify PF4 amino acids essential for binding pathogenic HIT antibodies. Methods Alanine scanning mutagenesis was utilized to produce 70 single point mutations of PF4. Each PF4 mutant was used in an enzyme immunoassay (EIA) to test their capacity to bind a platelet-activating murine monoclonal anti-PF4/heparin antibody (KKO) and HIT patient sera (n = 9). Results and Conclusions We identified 13 amino acids that were essential for binding KKO because they directly affected either the binding site or the antigenic conformation of PF4. We also identified 10 amino acids that were required for the binding of HIT patient sera and five of these amino acids were required for binding both KKO and the HIT patient sera. The 10 amino acids required for binding HIT sera were further tested to differentiate pathogenic HIT antibodies (platelet activating, n = 45) and non-pathogenic antibodies (EIA-positive but not platelet activating, n = 28). We identified five mutations of PF4 that were recognized to be essential for binding pathogenic HIT antibodies. Using alanine scanning mutagenesis, we characterized possible binding sites of pathogenic HIT antibodies on PF4.

The mechanisms of platelet underproduction in immune thrombocytopenia (ITP) remain unknown. While the number of megakaryocytes is normal or increased in ITP bone marrow, further studies of megakaryocyte integrity are needed. Megakaryocytes are responsible for the production of platelets in the bone marrow, and they are possible targets of immune-mediated injury in ITP. Since the biological process of megakaryocyte apoptosis impacts platelet production, we investigated megakaryocyte DNA fragmentation as a marker of apoptosis from ITP bone marrow biopsies. Archived bone marrow biopsy specimens from ITP patients, bone marrow specimens from controls with normal platelet counts, and bone marrow specimens from thrombocytopenic controls with myelodysplastic syndrome (MDS) were evaluated. Sections were stained with anti-CD61 for megakaryocyte enumeration, and terminal deoxynucleotidyl transferase dUTP nick-end labeling was used as an apoptotic indicator. In ITP patients, megakaryocyte apoptosis was reduced compared to nonthrombocytopenic controls. Megakaryocyte apoptosis was similarly reduced in thrombocytopenic patients with MDS. These results suggest a link between megakaryocyte apoptosis and platelet production.

BACKGROUND Cultured megakaryocytes could prove useful in the study of human diseases, but it is difficult to produce sufficient numbers for study. We describe and evaluate the use of an expansion process to develop mature megakaryocytes from peripheral blood–derived human hematopoietic stem and progenitor cells (HSPCs). STUDY DESIGN AND METHODS HSPCs (CD34+) were isolated from peripheral blood by positive selection and expanded using an optimal CD34+ expansion supplement. We evaluated megakaryocyte growth, maturation, and morphology in response to thrombopoietin (TPO) stimulation using flow cytometry and electron microscopy. TPO demonstrated a dose-dependent stimulatory effect on both megakaryocyte number and maturation. RESULTS From 90 to 120 mL of unmanipulated peripheral blood, we isolated a mean of 1.5 × 105 HSPCs (1.5 × 103 cells/mL of whole blood). HSPCs expanded nine-fold after a 4-day culture using an expansion supplement. Expanded cells were cultured for an additional 8 days with TPO (20 ng/mL), which resulted in a 2.9-fold increase in megakaryocytic cells where 83% of live cells expressed CD41a+, a marker of megakaryocyte commitment, and 50% expressed CD42b+, a marker for megakaryocyte maturation. The expanded HSPCs responded to TPO stimulation to yield more than 1.0 × 106 megakaryocytes. This cell number was sufficient for morphologic studies that demonstrated these expanded HSPCs produced mature polyploid megakaryocytes capable of forming proplatelet extensions. CONCLUSIONS Peripheral blood HSPCs can be expanded and differentiated into functional, mature megakaryocytes, a finding that supports the use of this process to study inherent platelet (PLT) production disorders as well as study factors that impair normal PLT production.

BACKGROUND Thrombopoietin receptor agonists are new treatments for patients with chronic immune thrombocytopenia (ITP). How one of these agent, romiplostim, has impacted practice patterns, especially the use of intravenous immune globulin (IVIG), has not been evaluated outside of clinical trials. STUDY DESIGN AND METHODS This was a retrospective cohort study of adult ITP patients treated with romiplostim in four Canadian centers. Patients had primary or secondary ITP and were followed for 1 year before starting weekly romiplostim treatment. We compared IVIG use, clinical outcomes, and cost before and after romiplostim. RESULTS Twenty-nine patients with ITP received romiplostim. Median age was 54 years (interquartile range [IQR], 45-63 years) and patients had a median of two prior ITP treatments (IQR, 1-4) including splenectomy (n = 7). Median platelet (PLT) count was 23 × 109 before and 124 × 109 after romiplostim. Median duration of romiplostim treatment was 3.7 months. Patients used a median of two IVIG infusions per year before and 0.7 per year after starting romiplostim (p = 0.16). For patients who received weekly romiplostim for at least 1 month (n = 19), IVIG infusions were three (IQR, 1-5) per year before and 0.7 (IQR, 0.4-1.6) per year after romiplostim. Results were squewed by two high IVIG users. Nineteen (66%) patients discontinued romiplostim treatment during follow-up because of lack of response (n = 8), sustained response (n = 5), toxicities (n = 4), or response to splenectomy (n = 2). Overall health care costs were similar before and after romiplostim when concomitant treatments, nursing resources, and hospitalizations were considered. CONCLUSIONS Romiplostim was associated with improved PLT counts and fewer IVIG infusions for most ITP patients. In practice, romiplostim was generally not continued long term and was cost neutral for overall ITP management.

Heparin-induced thrombocytopenia (HIT) is caused by platelet-activating antibodies against complexes of platelet factor 4 (PF4) and heparin. The diagnosis of HIT is contingent on accurate and timely laboratory testing. Recently, alternative anticoagulants for the treatment of HIT have been introduced along with algorithms for better HIT diagnosis. However, the increased reliance on immunoassays for the diagnosis of HIT may have harmful consequences due to the high rate of false positive results. To compare trends and implications of current HIT testing approaches, we analyzed results over a six-year period from the McMaster University Platelet Immunology Reference Laboratory. From 2008 to 2013, 8,546 samples were investigated for HIT using both an in-house IgG-specific anti-PF4/heparin enzyme immunoassay (EIA) and the serotonin-release assay (SRA). Of 8,546 samples tested, 13.4% were true-positives (positive in both assays); 65.6% were true-negatives (negative in both assays); 20.9% were presumed false positive for HIT (EIA-positive/SRA-negative); and 0.2% were EIA-negative/SRA-positive. The frequency of EIA-positive/SRA-negative results increased over time (from 12.9% in 2008 to 22.9% in 2013). We found that the number of SRA-negative samples was reduced from referring centers that used an immunoassay as an initial screen; however, 41% of those samples tested negative in the immunoassay and in the SRA at the reference laboratory. The suspicion of HIT continues at a high rate and the agreement between the EIA and SRA test results remains problematic. Am. J. Hematol. 90:629–633, 2015. © 2015 Wiley Periodicals, Inc.

The primary objective of this phase II study was to evaluate the efficacy of rituximab in the management of adult patients with physician-diagnosed presumed thrombotic thrombocytopenic purpura (TTP); relapsed or refractory. We conducted a multicentre study in four Canadian hospital-based apheresis units. Forty patients with presumed TTP (20 refractory and 20 relapsing) were sequentially enrolled and all received rituximab in a standardized manner. A complete response was documented in 14 of 19 refractory patients by week 8 and 15/16 were alive and in remission at 52 weeks (one patient was lost to follow-up, one was a non-responder, and three died). Among relapsing patients, 16/18 had a complete response at week 8 and 18/18 at week 52 (one patient lost to follow-up and one withdrew). At 1 year, all relapsing and 85% of refractory patients survived. Of 38/40 patients who had ADMATS13 testing at study entry, 13/19 refractory and 10/19 relapsing patients had ADAMTS13 10% (typical TTP); whereas 6/19 refractory and 9/19 relapsing cases had ADAMTS13 10% (other thrombotic microangiopathy; TMA). Refractory-typical TTP in contrast to refractory-other TMA and all relapsing patients treated with plasma exchange and rituximab, were less likely to be responsive and more likely to die or relapse.

The burden of severe bleeding in adults and children with immune thrombocytopenia (ITP) has not been established.To describe the frequency and severity of bleeding events in patients with ITP, and the methods used to measure bleeding in ITP studies.We performed a systematic review of all prospective ITP studies that enrolled 20 or more patients. Two reviewers searched Medline, Embase, CINAHL and the Cochrane registry up to May 2014. Overall weighted proportions were estimated using a random effects model. Measurement properties of bleeding assessment tools were evaluated.We identified 118 studies that reported bleeding (n = 10 908 patients). Weighted proportions for intracerebral hemorrhage (ICH) were 1.4% for adults (95% confidence interval [CI], 0.9-2.1%) and 0.4% for children (95% CI, 0.2-0.7%; P0.01), most of whom had chronic ITP. The weighted proportion for severe (non-ICH) bleeding was 9.6% for adults (95% CI, 4.1-17.1%) and 20.2% for children (95% CI, 10.0-32.9%; P0.01) with newly-diagnosed or chronic ITP. Methods of reporting and definitions of severe bleeding were highly variable in primary studies. Two bleeding assessment tools (Buchanan 2002 for children; Page 2007 for adults) demonstrated adequate inter-rater reliability and validity in independent assessments.ICH was more common in adults and tended to occur during chronic ITP; other severe bleeds were more common in children and occurred at all stages of disease. Reporting of non-ICH bleeding was variable across studies. Further attention to ITP-specific bleeding measurement in clinical trials is needed to improve standardization of this important outcome for patients.

Heparin-induced thrombocytopenia (HIT) is an adverse drug reaction characterized by IgG antibodies bound to complexes of platelet factor 4 (PF4) and heparin. The majority of diagnostic tests for HIT rely on an exogenous source of PF4 to identify anti-PF4/heparin antibodies. These include the PF4-dependent enhanced serotonin release assay (PF4-SRA) among others. Using a bacterial expression system, we developed a novel and efficient method of producing recombinant human PF4 (rhPF4) that is biochemically and antigenically similar to platelet-derived human PF4. rhPF4 was produced using the pET expression system in the BL21(DE3) strain of Escherichia coli. The system was optimized for protein expression using isopropyl β-D-1-thiogalactopyranoside at different induction temperatures and incubation times. rhPF4 solubility was improved by using different detergents during cell lysis and by purifying with heparin affinity and ion exchange chromatography. Biochemical characteristics of rhPF4 were investigated using mass spectrometry, SDS-PAGE analysis, and gel filtration chromatography and compared to platelet-derived PF4. Antigenic and functional characteristics of rhPF4 were studied using the anti-PF4/heparin EIA and the PF4-SRA. Using this method, we could produce 11.4 ± 0.6 mg of pure rhPF4 per liter of bacterial culture. Absorbance readings from the anti-PF4/heparin EIA using platelet-derived and rhPF4 were highly correlated (n = 194; r = 0.9545, p 0.0001); and functional release of serotonin in the PF4-SRA induced by anti-PF4/heparin antibodies was similar to either platelet-derived or rhPF4 and heparin (r = 0.9597, p 0.0001). Our method of rhPF4 production is efficient and does not rely on a source of platelets. The rhPF4 purification method described produces greater yields at a lower cost than other current methods. The application of this method can improve the efficiency of biochemical investigations and HIT diagnostic testing by supplying sufficient amounts of PF4.

Autoantibodies to thrombopoietin (TPO, also termed THPO) or the TPO receptor (cMpl, also termed MPL) could play a pathological role in immune thrombocytopenia (ITP). In this study, we tested for autoantibodies against TPO, cMpl, or the TPO/cMpl complex in ITP and other thrombocytopenic disorders. Using an inhibition step with excess TPO in fluid-phase to improve binding specificity, the prevalence of anti-TPO autoantibodies was: active ITP: 9/32 (28%); remission ITP: 0/14 (0%); non-immune thrombocytopenias: 1/10 (10%); and healthy controls: 1/11 (9%). Similarly, using an inhibition step with excess cMpl, the prevalence of specific anti-cMpl autoantibodies was: active ITP: 7/32 (22%); remission ITP: 1/14 (7%); non-immune thrombocytopenias: 3/10 (30%); and healthy controls: 0/11 (0%). Two active ITP patients had autoantibodies against the TPO/cMpl complex, but not against TPO or cMpl alone. Anti-TPO or anti-cMpl autoantibodies were found in 44% of ITP patients, and in 40% of patients with other thrombocytopenic disorders. These autoantibodies did not correlate with ITP disease severity or number of ITP treatments received; however, in this cohort, 3 patients failed to respond to TPO receptor agonist medications, and of those, 2 had anti-TPO autoantibodies. This suggests that anti-TPO and anti-cMpl autoantibodies are associated with thrombocytopenia, and may be clinically relevant in a subset of ITP patients.

Essentials The immunogenesis of Heparin-induced thrombocytopenia (HIT) is not well understood. Immunization to platelet factor 4 (PF4)-heparin occurs early in life, before any heparin exposure. PF4 and PF4-heparin complexes induce the proliferation of CD14+ cells. Reduced levels of regulatory cytokines contribute to immune dysregulation in HIT. Summary Background Heparin-induced thrombocytopenia (HIT) is an adverse reaction to heparin characterized by thrombocytopenia and thrombotic complications. HIT is caused by pathogenic antibodies that bind to complexes of platelet factor 4 (PF4) and heparin, leading to platelet activation and inducing a hypercoagulable state. Previous studies have shown immunity to PF4-heparin complexes occurs early in life, even before heparin exposure; however, the immunogenesis of HIT is not well characterized. Objectives To investigate cellular proliferation in response to PF4-heparin complexes in patients with HIT. Patients/Methods Peripheral blood mononuclear cells (PBMCs) from healthy controls (n = 30), postoperative cardiac surgery patients who had undergone cardiopulmonary bypass (CPB) (n = 17) and patients with confirmed HIT (n = 41) were cultured with PF4 and PF4-heparin complexes. Cellular proliferation was assessed by [3 H]thymidine uptake and 5-ethynyl-2'-deoxyuridine detection. Results and Conclusions PBMCs proliferated in the presence of PF4, and this was enhanced by the addition of heparin in all study groups. CPB and HIT patients showed significantly greater proliferative responses than healthy controls. PBMC proliferation was antigen-specific, depended on the presence of platelets, and only CD14+ cells were identified as proliferating cells. Culture supernatants were tested for the levels of regulatory cytokines, and both CPB and HIT patients produced significantly lower levels of interleukin-10 and transforming growth factor-β1 than healthy controls. These findings further demonstrate cellular immune sensitization to PF4-heparin complexes occurs before heparin exposure, and suggests immune dysregulation can contribute to HIT.

Nonspecific diagnostic criteria and uncertain estimates of severe bleeding events are fundamental gaps in knowledge of primary immune thrombocytopenia (ITP). To address these issues, we created the McMaster ITP Registry. In this report, we describe the methodology of the registry, the process for arriving at the diagnosis, and the frequency of bleeding. Consecutive patients with platelets 1 visit was 1.7 years (interquartile range, 0.8-3.4). At registration, 295 patients were initially diagnosed with primary ITP; of those, 36 (12.2%) were reclassified as having a different diagnosis during follow-up. At registration, 319 patients were initially diagnosed with another thrombocytopenic condition; of those, 10 (3.1%) were ultimately reclassified as having primary ITP. Of 269 patients with a final diagnosis of primary ITP, 56.5% (95% confidence interval [CI], 50.4-62.5] experienced grade 2 bleeding at 1 or more anatomical site, and 2.2% (95% CI, 0.8-4.8) had intracranial hemorrhage. Nearly 1 in 7 patients with primary ITP were misdiagnosed. Grade 2 bleeding was common. Registry data can help improve the clinical and laboratory classification of patients with ITP.

Primary immune thrombocytopenia (ITP) is caused by platelet autoantibodies and T-cell dysregulation. Both platelets and their precursor megakaryocytes may be targeted leading to platelet destruction and underproduction. Current treatments for ITP are inadequate since they do not reverse the disease process and generally do not result in durable remissions. In addition, many treatments are limited by side effects including infection and potentially thrombosis. Novel agents that are currently in development target certain key steps in the disease process, including: (1) the interaction between T-cell and antigen presenting cells (CD40–CD154 interaction); (2) the binding of the Fc portion of platelet autoantibodies to Fc-receptors on macrophages (soluble Fc-RIIb); and (3) the signaling pathways leading to platelet phagocytosis by macrophages (Syk inhibition). Other strategies have been to augment platelet production by simulating thrombopoiesis or by neutralizing physiological inhibitors of megakaryopoiesis. Targeted therapies in ITP have the potential to improve disease morbidity and mortality while limiting systemic side effects. Before these agents can be used in practice, additional clinical studies are needed with rational study outcomes including platelet count, bleeding and quality of life. An individualized treatment strategy is needed for patients since ITP is a distinctly heterogeneous disease.

Background: Patients with immune thrombocytopenia (ITP) may require treatment to raise the platelet count before surgery. Intravenous immune globulin (IVIG) is commonly used for this purpose, but eltrombopag, an oral thrombopoietin receptor agonist, may be a good alternative. We compared perioperative eltrombopag or IVIG for the achievement of platelet count targets for major or minor surgery. Methods: We conducted a randomized, non-inferiority trial at 8 centers in Canada.ITP patients with a platelet count Results: From 2013 to 2019, 38 patients were assigned to received eltrombopag and 36 patients were assigned to receive IVIG before major (n= 31) or minor (n= 43) surgery. Five patients did not complete the study. By intention to treat, 30/38 (78.9%) patients on eltrombopag achieved perioperative platelet count targets compared with 22/36 (61.1%) on IVIG (absolute risk difference, 17.8%; one-sided lower limit of the 95% confidence interval, 0.4%; p=0.005 for non-inferiority). Results were similar in the per protocol analysis (absolute risk difference: 15.8%; one-sided lower limit of the 95% CI, -2.1%; p=0.009). Eltrombopag was superior to IVIG in the intention-to-treat analysis (p=0.047) but not in the per-protocol analysis (p =0.074). One patient developed pulmonary embolism 14 days after minor surgery (skin biopsy) and 7 days after stopping eltrombopag when the platelet count was 135 x109/L. Of 18 patients who underwent splenectomy on study, marked post-splenectomy thrombocytosis (platelets >1,000 x109/L) occurred in 2 (11.1%) patients, both of whom were on eltrombopag. Global treatment satisfaction scores were higher for eltrombopag. Conclusion: Eltrombopag is non-inferior and may be superior to IVIG for achieving target platelet counts perioperatively for patients with ITP. Post-operative thromboprophylaxis should be considered with eltrombopag. Funding Source:This was an investigator-initiated trial funded by Novartis. Disclosures Arnold: Novartis: Honoraria, Research Funding; Rigel: Consultancy, Research Funding; Bristol-Myers Squibb: Research Funding; Principia: Consultancy. Heddle:Novartis: Research Funding. Hsia:Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees; Pfizer: Membership on an entity's Board of Directors or advisory committees; Amgen: Honoraria; Jansen: Honoraria, Membership on an entity's Board of Directors or advisory committees. Sholzberg:Novartis: Honoraria; Amgen: Honoraria, Research Funding. Lin:Pfizer: Consultancy; Novartis: Research Funding; Octapharma: Research Funding; Amgen: Consultancy. Larratt:Novartis: Honoraria. Amini:Amgen NL: Research Funding; Novartis NL: Research Funding. Schipperus:Novartis: Research Funding. Lim:Pfizer Canada: Consultancy, Honoraria; Portola Pharmaceuticals: Consultancy; Bristol-Myers Squibb: Honoraria. OffLabel Disclosure: Eltrombopag is not licenced for perioperative treatment in patients with ITP.