Heparin-induced thrombocytopenia, Part 1: The diagnostic clues: An abrupt decline in platelet count is telling

Mild to moderate thrombocytopenia that is complicated by thrombosis is the typical presentation of immune-mediated heparin-induced thrombocytopenia (HIT). Usually, the platelet count begins to fall 5 to 10 days after a patient begins to receive heparin. However, if the patient has received heparin within the previous 100 days and significant levels of HIT antibodies are still present, the platelet count fall can be abrupt when heparin is given again. Careful assessment for thrombosis should be performed when evaluating a patient who may have HIT. Generally, negative results from highly sensitive assays for HIT antibodies (such as the combination of a platelet factor 4-dependent immunoassay and a washed platelet activation assay) using blood samples obtained during thrombocytopenia excludes HIT.