A flow cytometric assay of platelet activation marker P-selectin (CD62P) distinguishes heparin-induced thrombocytopenia (HIT) from HIT with thrombosis (HITT)

Heparin induced thrombocytopenia (HIT) is a well-known complication of hepa rin administration but usually resolves upon discontinuation without sequel ae. However, a small proportion of HIT patients develop thrombosis associat ed with HIT, designated as HITT, which is often life-threatening and may le ad to gangrene and amputations. Existing laboratory methods of confirming H IT/HITT do not distinguish between HIT and HITT. We report a flow cytometri c assay of platelet activation marker CD62P to distinguish the effects of a ddition of HIT vs. HITT plasma to normal blood. Briefly, normal whole blood was incubated with platelet-poor plasma from 12 patients with HITT, 30 wit h HIT, and 65 controls, in presence and absence of heparin, and expression of CD62P was assayed by flow cytometry. When the ratios of fluorescent inte nsity of CD62P with heparin divided by that without heparin were compared, HITT plasma induced significantly higher ratios than HIT plasma (HITT ratio s similar to 2.5 vs. HIT ratios similar to 1.2; p < 0.001). Eleven of 12 HI TT patients were positive by this test but only 5 of 30 HIT patients were p ositive (p < 0.0005). In a case of HIT with silent thrombosis, this assay g ave a positive results prior to clinically evident thrombosis. In conclusio n, this method distinguishes HITT from HIT and may be clinically useful in the detection of HITT, allowing early intervention for preventing catastrop hic thrombosis.