A series of laboratory tests can aid in the evaluation of patients with possible heparin-induced thrombocytopenia.



(1) platelet activation tests

(1a) platelet aggregation testing

(1b) serotonin release assay

(2) heparin-platelet factor 4 (heparin-PF4) ELISA assay


Testing Sequence


Step 1: Perform an initial platelet activation test (platelet aggregation or serotonin release) and the heparin-platelet factor 4 assay

(1a) If both tests are positive, then heparin-induced thrombocytopenia is likely.

(1b) If both tests are negative, then heparin-induced thrombocytopenia is unlikely.

(1c) If one or the other test is positive, proceed to Step 2.


Step 2: Perform the other platelet activation test not performed in Step 1.

(2a) If the second platelet activation test is negative, then the diagnosis of heparin induced thrombocytopenia is uncertain.

(2b) If the second platelet activation test is positive, then interpret according to the following table.


Initial Platelet Activation Test

Heparin-PF4 Assay




antibodies with other specificities



probable heparin-induced thrombocytopenia



• antibodies with other specificities include antibodies to interleukin 8 (IL-8)


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