Differentials
Postoperative state
SIGNS / SYMPTOMS
It is not uncommon for the platelet count to initially fall after surgery and then rise to a level higher than the preoperative count (rebound thrombocytosis).
The postoperative rebound platelet count should be considered the new baseline count in these patients when determining the clinical probability of HIT. This is particularly noteworthy in patients undergoing cardiovascular surgery who commonly form HIT antibodies (due to exposure to high doses of heparin), but rarely develop clinical evidence of HIT.
INVESTIGATIONS
Thrombocytopenia due to surgery usually occurs within the first 24-48 hours and recovers spontaneously.
Thrombocytopenia that begins >4 days after surgery or lasts for >4 days after surgery should raise suspicion of HIT.
Thrombotic thrombocytopenic purpura
SIGNS / SYMPTOMS
New severe neurologic abnormalities, with or without fever and signs of anemia.
INVESTIGATIONS
HIT assay test negative for HIT antibodies.
Microangiopathic hemolytic anemia with schistocytes on examination of peripheral blood smear.
Normal coagulation parameters.
Drug-induced thrombocytopenic purpura
SIGNS / SYMPTOMS
A thorough medical history is needed to identify potential drugs (e.g., vancomycin, carbamazepine, sulfa drugs, antineoplastic agents, glycoprotein IIb/IIIa antagonists, quinine/quinidine).
Platelet nadir may be <20 × 10⁹/L (rare in HIT).
Petechiae may be present.
INVESTIGATIONS
No differentiating tests.
Sepsis/severe infection
SIGNS / SYMPTOMS
Septic patients tend to have hypotension, fever, and other signs of organ dysfunction.
Evidence of disseminated intravascular coagulation may also be present in patients with severe HIT.
INVESTIGATIONS
HIT assay test negative for HIT antibodies.
Positive blood cultures.
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