BACKGROUND: Heparin-induced thrombocytopenia (HIT) is a possible complication of heparin therapy that can evolve with life-threatening thromboembolism, for which early diagnosis is essential. However, the specific laboratory approach to the diagnosis of HIT is still controversial. METHODS: Sera from 13 patients with HIT, from 15 patients with non-HIT thrombocytopenia, and from 10 normal subjects were used to compare nonfunctional and functional methods to detect anti-heparin:PF-4 antibodies and platelet activation. We used three enzyme-linked immunosorbent assays (ELISAs) and the particle gel immunoassay as nonfunctional tests, and platelet aggregometry, CD62p (p-selectin) phenotypical expression, and Annexin V binding as functional assays. RESULTS: CD62p expression was positive in 85% of the cases and Annexin V was positive in 40% of the HIT cases examined. Aggregometry gave variable results that depend strongly on the donor. CONCLUSION: Functional tests for platelet activation are more reliable for HIT diagnosis than the nonfunctional tests. We conclude that the phenotypical expression of p-selectin detected by flow cytometry on activated platelets appears to be a good functional marker for the diagnosis of HIT and its possible thromboembolic complications.
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