Laboratory tests for the diagnosis of heparin-induced thrombocytopenia

Heparin-induced thrombocytopenia (HIT) is associated with high morbidity an d mortality. Because the pathophysiology of this complex disorder has remai ned unclear, so has the development of supportive diagnostic laboratory ass ays. The currently available laboratory methods for HIT diagnosis include s everal platelet function assays: the platelet aggregation assay, platelet a ggregation with simultaneous measurement of ATP release (lumi-aggregometry) , the serotonin release assay, and flow cytometric assays. ELISA assays, wh ich quantitate anti-heparin/platelet factor 4 antibody titers, have recentl y become available. Assay characteristics for these assays were studied usi ng sera collected from clinically diagnosed HIT patients with and without t hrombosis, normal individuals, various types of hospitalized patients witho ut HIT, heparin or low molecular weight heparin-treated patients without HI T; and patients with platelet-immune disorders other than HIT. The results of our studies suggest that none of the assays can be considered a "gold st andard" for the laboratory diagnosis of HIT as many false-negative and fals e-positive results were obtained. Furthermore, antibodies against the hepar in/platelet factor 4 complex, as identified by the current ELISA tests, are not the sole cause of HIT since many patients lacking clinical symptoms as sociated with HIT exhibited high antibody titers following heparin treatmen t, An assay using flow cytometry, being developed for HIT testing, will be described. At this time, clinical impression remains important for the diag nosis of HIT.