Survey report on functional tests in heparin-induced thrombocytopenia: communication from the ISTH SSC subcommittee on immune-mediated platelet disorders.

Heparin-induced thrombocytopenia (HIT) is a severe, immune-mediated adverse drug reaction characterized by platelet-activating antibodies produced in response to heparin therapy, leading to thrombocytopenia and an increased risk of thrombosis. Functional assays are critical for confirming HIT but remain challenged by significant inter-laboratory variability that undermines diagnostic accuracy and reproducibility. This study aimed to evaluate current functional HIT testing and identify areas for standardization. A structured electronic survey was distributed to laboratories performing functional HIT testing, with responses collected over a four-week period. Substantial heterogeneity was observed in protocols, including variations in platelet donors and preparation methods, heparin concentrations, FcγRIIA blockade, and internal quality control procedures. Although most laboratories employed multiple heparin concentrations to improve performance, inconsistencies in other critical assay parameters persisted. These inconsistencies highlight the need for harmonized functional testing protocols to improve assay comparability, diagnostic precision, and patient outcomes.