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Accurate serum cryoglobulin detection is important to allow prompt treatment but laboratory testing requires stringent pre-analytical conditions and has long turnaround times. Serum protein electrophoresis (EPG) for paraproteinaemia and rheumatoid factor (RF) analysis may offer an effective initial screening strategy for the presence of cryoglobulinaemia. We retrospectively assessed the sensitivity of ancillary EPG and RF testing for the presence of serum cryoglobulinaemia in 586 eligible cryoglobulin positive samples received at the Royal Prince Alfred and Liverpool Hospital immunopathology laboratories over an 11-year period. Ninety-one percent of all cryoglobulin positive samples had either a detectable paraprotein or RF activity, with greatest sensitivity for type I and type II cryoglobulins (97% and 98%, respectively). The sensitivity remained high irrespective of whether EPG and RF analysis was performed with the same, or different, pre-analytical collection conditions to the cryoglobulin collection (92% vs 90%, p=0.46). Only two patients with detected cryoglobulins and no associated paraprotein or RF activity had clinical features of cryoglobulinaemia and neither required treatment. This study demonstrates that serum EPG and RF analysis has high sensitivity for the detection of clinically relevant cryoglobulinaemia, even when not collected under ideal pre-analytical conditions, and potentially offers a prompt and effective screening strategy., (Crown Copyright © 2022. Published by Elsevier B.V. All rights reserved.)

Three commercially available assays for the measurement of antibodies to infliximab (ATI) are approved for clinical use in Australia: Promonitor anti-infliximab (Grifols), Lisa Tracker anti-infliximab (Theradiag) and Ridascreen anti-IFX (R-Biopharm). All are bridging ELISA assays. Measurement of ATI has been incorporated into treatment algorithms for assessing loss of response to infliximab in patients with inflammatory bowel disease, but results obtained by the three ATI assays have not been systematically compared. We performed a series of experiments to allow comparison of results between the assays. Forty-two patient samples known to be positive for ATI by the Lisa Tracker assay were run on the Promonitor assay in singlicate, of which 26 were run on the Ridascreen assay in duplicate, according to the manufacturers' instructions. The Spearman correlation coefficient for all three pairwise assay comparisons was 0.95. Results were not numerically comparable between the assays. The coefficient of variation (CV) was 2.3% for the Lisa Tracker assay, 7.6% for the Promonitor assay and 7.4% for the Ridascreen assay. The presence of infliximab interfered with all three assays in a dose dependent manner. The cut-point for loss of response to infliximab dose intensification, previously demonstrated to be 200 ng/mL on the Lisa Tracker assay, is equivalent to approximately 60 ng/mL on the Ridascreen assay and between 22.9 and 41 AU/mL on the Promonitor assay. All three assays are suitable for clinical use., (Crown Copyright © 2020. Published by Elsevier B.V. All rights reserved.)