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Heparin thromboprophylaxis is routinely administered during hospitalization for COVID-19. Because of the immune stimulation related to COVID-19, there is ongoing concern regarding a heightened incidence of heparin-induced thrombocytopenia (HIT). We performed a literature search using PubMed, EMBASE, Cochrane, and medRxiv database to identify studies that reported clinical and laboratory characteristics and/or the incidence of HIT in patients with COVID-19. The primary aim was to systematically review the clinical features and outcomes of patients with COVID-19 with confirmed HIT. The secondary objective was to perform a meta-analysis to estimate the incidence of HIT in hospitalized patients with COVID-19. A meta-analysis of 7 studies including 5849 patients revealed the pooled incidence of HIT in COVID-19 of 0.8% (95% confidence interval [CI], 0.2%-3.2%; I2 = 89%). The estimated incidences were 1.2% (95% CI, 0.3%-3.9%; I2 = 65%) vs 0.1% (95% CI, 0.0%-0.4%; I2 = 0%) in therapeutic vs prophylactic heparin subgroups, respectively. The pooled incidences of HIT were higher in critically ill patients with COVID-19 (2.2%; 95% CI, 0.6%-8.3%; I2 = 72.5%) compared with noncritically ill patients (0.1%; 95% CI, 0.0%-0.4%: I2 = 0%). There were 19 cases of confirmed HIT and 1 with autoimmune HIT for clinical and laboratory characterization. The median time from heparin initiation to HIT diagnosis was 13.5 days (interquartile range, 10.75-16.25 days). Twelve (63%) developed thromboembolism after heparin therapy. In conclusion, the incidence of HIT in patients with COVID-19 was comparable to patients without COVID-19, with higher incidences with therapeutic anticoagulation and in critically ill patients., (© 2021 by The American Society of Hematology. Licensed under Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0), permitting only noncommercial, nonderivative use with attribution. All other rights reserved.)

Venous thromboembolism (VTE) is a common cause of cardiovascular morbidity and mortality. Heparins and warfarin have been the standard treatment of VTE for decades, but they have several disadvantages, e.g. parenteral route, narrow therapeutic window and numerous drug interactions. The development of new, non-vitamin K antagonist oral anticoagulants (NOACs) that can overcome these problems is a significant breakthrough and may replace warfarin for treatment of VTE. However, NOACs have some limitations, e.g. the lack of antidotes and high cost. As a result, many physicians are uncomfortable to employ NOACs in daily practice. This review will briefly summarize and update pharmacological profiles, evidence base for VTE treatment from Phase III clinical trials and some clinical considerations of NOACs in treatment of VTE.

Background: Solid tumor is the strongest risk factor for VTE in Thai medical in-patients. This study aimed to identify the markers predicting symptomatic VTE in this group., Methods: Solid tumor patients admitted to the medical wards from June 2007 to December 2009 were monitored for VTE symptoms, excluding patients with VTE on admission. Anticoagulant prophylaxis was not given. Cases were all symptomatic VTE within 6 weeks after discharge. The controls were active solid tumor in-patients admitted in 2009 and did not develop VTE. The cases and controls were compared for the risk factors of VTE and complete blood count (CBC) on admission., Results: There were 28 radiology-confirmed VTE cases during the 2.5-year study period. There were 280 solid tumor patients without VTE as the controls. There was no difference in age (58.4 vs. 61.6 years), sex (53.6% vs. 64.3% male), presence of leg paralysis, acute infection and obesity between cases and controls, respectively. The cases showed higher absolute monocyte counts compared with the controls (0.76 vs. 0.56×10(9)/L, p 0.013), but there were no differences in other CBC parameters. In a multivariate analysis, cancer of unknown primary (Odds ratio [OR] 13.7, 95% confidence interval [CI] 2.74-68.7, p 0.001), biliary cancer (OR 6.6, 95% CI 1.80-24.3, p 0.004) and a monocyte count over 0.5×10(9)/L (OR 5.0, 95% CI 1.62-15.5, p 0.005) significantly associated with VTE., Conclusion: Metastatic diseases with obscured primary sites, biliary carcinomas and higher monocyte counts on admission are related to subsequent VTE in hospitalized cancer patients., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

Thromboprophylaxis for venous thromboembolism (VTE) failed to reduce overall mortality in hospitalised medical patients. As a VTE prediction model for Asians is still lacking, this study aimed to identify very high risk patients who would be the main target for prevention. In 2009, medical patients admitted to King Chulalongkorn Memorial hospital, a tertiary care centre, were prospectively evaluated for risk factors. The high-risk cohort was monitored for symptomatic VTE until six weeks after discharge. No heparin prophylaxis was given. Of 1,290 high-risk patients, 27 (2.1%, 95% confidence interval [CI] 1.3-2.9) developed proven VTE, 25.9% of which were diagnosed after discharge. Cases with VTE stayed longer in the hospital (median 18 vs. 11 days, p < 0.001). The significant risk factors in a multivariate analysis were autoimmune disease, solid tumours, family history of VTE, varicose vein and oestrogen with the relative risks of 11.8, 4.7, 120.3, 40.1 and 17.1 (p < 0.001, 0.001, 0.001, 0.002 and 0.038), respectively. Either autoimmune disease or solid tumours were found in 63% of VTE with the relative risk of 4.5 (95% CI 2.1-9.7, p < 0.001). In contrast, previously reported VTE scores in western patients could not stratify the VTE risks, but all the scores predicted higher mortality. In conclusion, VTE is common in Asian hospitalised medical patients. Patients with autoimmune disease and those with solid tumours are highly susceptible to VTE. A prophylactic strategy in these groups is required.

Patients with multiple myeloma are at increased risk of venous thromboembolism (VTE) compared to the general population. The introduction of immunomodulatory agents, such as thalidomide and lenalidomide, substantially increases the incidence of VTE in multiple myeloma patients, especially when used in combination with high-dose dexamethasone and/or anthracycline-based chemotherapy. Thromboprophylaxis is recommended for reducing VTE in patients receiving immunomodulatory agent-based regimens. On the other hand, bortezomib, a proteasome inhibitor, is not associated with an increased risk of VTE, as observed by a very low incidence of thrombotic complications in the absence of thromboprophylaxis. Currently, the mechanisms underlying the impact of these agents on VTE are not well-understood. Further studies to investigate the pathogenesis of VTE in multiple myeloma are warranted. These studies may not only yield greater insight into the pathogenesis of disease but may also define novel targets for the prevention and treatment of thromboembolic events in patients with multiple myeloma., (Copyright 2010 Elsevier Ltd. All rights reserved.)