Subcommittee on Platelet Immunology: Heparin-induced multi electrode aggregometry method for heparin-induced thrombocytopenia testing Heparin-induced thrombocytopenia (HIT) is a rare life-threatening complication of exposure to unfractionated/LMW heparin. HIT diagnosis remains challenging, needing careful review of the clinical history and sensitive laboratory assays. Pre-test clinical scores are based on timing and depth of thrombocytopenia and guide testing strategies. Many immunoassays are available to detect the presence of anti-PF4/heparin antibodies, including on-demand assays. A negative immunoassay result can be used to exclude HIT, but positive results include many patients with non-pathogenic antibodies (false positive HIT). The modest specificity of current immunoassays means overdiagnosis is common, leading to unnecessary treatments, increasing costs and bleeding risk. Functional assays which detect platelet activating heparin-dependent antibodies (SRA,HIPA) can confirm HIT, but are technically demanding and limited to expert laboratories. Read more.