Improved laboratory confirmation of heparin-induced thrombocytopenia type II - Time course of antibodies and combination of antigen and biologic assays

We studied whether laboratory confirmation of heparin-induced thrombocytope nia (HIT) can be improved after antigen clearance by determining free antib ody and combining the results of an antigenic and a biologic assay. Blood s amples taken over 40 days in 14 patients with HIT with thromboembolism unde rwent fluorescence-linked immunofiltration and the carbon 14-serotonin rele ase assays. Of the 14 patients, 11 showed positive results in both assays at day 1 afte r stopping heparin. The 3 patients with negative results seroconverted in o ne or both assays during the subsequent 7 days. Combining the positive resu lts of the assays increased the sensitivity from 85% at day 1 to 100% at da y 7. Assay results became negative in all patients within 40 days. The plat elet count normalized between days 2 and 9 after withdrawal of heparin. It is assumed that the free antibody can be detected after withdrawal of hepar in and after clearance of the platelet factor 4-heparin complex in patients with HIT.