Laboratory diagnosis of heparin-induced thrombocytopenia type II after clearance of platelet factor 4/heparin complex

Laboratory confirmation of heparin-induced thrombocytopenia (HIT) is limite d by assay sensitivity We investigated whether laboratory confirmation can be improved after antigen clearance by determining free antibody and combin ing the results of antigenic and biologic assays. Blood samples were collec ted over 5 to 6 weeks in 14 HIT patients. As an antigenic assay, the fluore scence-linked immunofiltration assay (FLIFA) was performed, and as a biolog ic assay, the carbon 14-labeled serotonin release assay was performed, At d ay 1 when heparin was stopped, 11 of 14 patients showed positive results in both assays; thus each assay had a sensitivity of 80%, The 3 patients with negative results seroconverted in one or both assays during the subsequent 7 days. Combining the positive results of the assays increased the sensiti vity to 100% at day 7, regardless of whether the antigenic or the biologic assay was performed first. Both assays became negative in all patients with in 5 to 6 weeks. The sensitivity of antigen and biologic assays in HIT pati ents increased to 100% after the time course of the heparin-induced antibod y. We assume that in some HIT patients the free antibody can be detected af ter withdrawal of heparin and after clearance of the platelet-factor 4/hepa rin complex.