Evaluation of a flow cytometric assay for the confirmation of heparin‐induced thrombocytopenia

Summary Introduction Heparin‐induced thrombocytopenia ( HIT ) is an immune‐mediated thrombocytopenia associated with heparin therapy. The diagnosis consists of a combination of pretest probability and laboratory testing. The routinely available laboratory antigen binding assays for the detection of specific antibodies have a low HIT ‐positive predictive value; therefore, to exclude false‐positive results, one of the functional assays should be performed. Functional assays evaluate the ability of heparin/ PF 4 antibodies to activate the platelets. The aim of our study was to validate the flow cytometric functional assay, based on the use of anti‐ CD 61 and anti‐ CD 62 antibodies, as a suitable diagnostic test for HIT . Methods Sera from patients with a clinical suspicion of HIT were previously analyzed with screening IgG‐specific ELISA , and 41 of those which were positive were selected for the functional assay. Results Our results were compared to another functional assay – the HIPA (heparin‐induced platelet aggregation assay). The diagnostic specificity of the flow cytometric assay was calculated based on HIPA results and was 83%. Conclusion Performing this functional test after the screening assay could significantly improve the specificity of HIT testing as heparin/ PF 4 antibodies are often not clinically significant.