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

ABSTRACT

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/PF4 antibodies to activate the platelets. The aim of our study was to validate the flow cytometric functional assay, based on the use of anti-CD61 and anti-CD62 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/PF4 antibodies are often not clinically significant.