The diagnosis of heparin-induced thrombocytopenia (HIT) requires exclusion of conditions that may mimic it. HIT can co-exist with any of these conditions.
General features of a mimic for HIT:
(1) onset after starting a heparin infusion
(2) presence of thrombocytopenia or unexplained drop in platelet count
(3) presence of thrombosis
The causes may be further classified based on the time of onset after initiation of heparin therapy.
number of days after starting heparin
Onset Type
0 - 4 days
early onset
>= 5 days
late onset
DIC-related causes:
(1) metastatic adenocarcinoma
(2) sepsis with purpura fulminans
Thrombo-embolic:
(1) pulmonary embolism
(2) infective endocarditis with arterial microthrombi
Hypercoagulable states:
(1) antiphospholipid antibody
(2) paroxysmal nocturnal hemoglobinuria (PNH)
Immune thrombocytopenia:
(1) post-transfusion purpura
Other:
(1) thrombolytic therapy
(2) diabetic ketoacidosis
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