PF4‐dependent P‐selectin expression assay in comparison to the heparin‐induced platelet activation assay for the diagnosis of heparin‐induced thrombocytopenia

Abstract Background Heparin‐induced thrombocytopenia (HIT) is a severe complication characterized by thrombocytopenia and thrombosis. The presence of antibodies against heparin/platelet factor 4 (PF4) complexes is a key indicator for HIT. Diagnostic laboratory testing generally includes detection of anti‐heparin/PF4 and/or functional testing such as the heparin‐induced platelet activation assay (HIPAA). However, current functional tests are time‐consuming and require specific technical skills. The PF4‐dependent P‐selectin expression assay (PEA) is a flow cytometry‐based test that evaluates activation of donor platelets in the presence of HIT patient serum. Methods We conducted the PEA with 23 patient sera that were positive in both the anti‐PF4/heparin enzyme‐linked immunosorbent assay (ELISA) and HIPAA and 26 sera that tested negative in the anti‐PF4/heparin ELISA. We next compared the PEA to the HIPAA using a retrospective clinical cohort of 195 sera of suspected HIT patients and tested the reproducibility of the PEA. Results The PEA was found to have a sensitivity of 73.9% and a specificity of 73.1% compared to the HIPAA. In our retrospective clinical cohort, we found that 74.4% (145 out of 195 samples) had identical results in both the HIPAA and PEA, with a specificity of 64.94% and sensitivity of 80.51% for the PEA compared to the HIPAA. Reproducibility testing of the PEA across three independent runs demonstrated consistent results in 83.3% (30 out of 36 samples). Discussion These findings suggest that the PEA is a promising functional test for HIT laboratory diagnostics based on the relatively high sensitivity; however, further studies are needed to validate its clinical applicability.