Cautions

Heparin-induced thrombocytopenia is a clinical diagnosis that is complemented by laboratory testing for antibodies to human platelet factor 4 (H/PF4) complexes and/or functional assays like the serotonin release assay. Assay results provide information on the presence or absence of H/PF4 antibodies, which are implicated in the pathogenesis of type II heparin-induced thrombocytopenia (HIT-II) with or without thrombosis. However, results of the H/PF4 antibody assay must be interpreted in conjunction with clinical findings (4T score) and other pertinent tests to evaluate other causes of thrombocytopenia (eg, sepsis, intravascular coagulation and fibrinolysis, thrombotic thrombocytopenic purpura, post-transfusion purpura, malignancy, drug-induced thrombocytopenia, autoimmune thrombocytopenia) or to confirm the findings of this assay.

Some low-titer, low-avidity antibodies and some antibodies that recognize sites on H/PF4 complex may not be detected using this assay.

Some patients may have naturally occurring antibodies to heparin PF4 (no evidence of heparin dependence) of no known significance with respect to pathogenesis of HIT-II.