Decision analysis for use of platelet aggregation test, carbon 14 serotonin release assay, and heparin-platelet factor 4 enzyme-linked immunosorbent assay for diagnosis of heparin-induced thrombocytopenia

The value of the platelet aggregation test, carbon 14-labeled serotonin rel ease assay (SRA), and heparin-platelet factor 4 enzyme-linked immunosorbent assay (H-PF4 ELISA) for the diagnosis of heparin-induced thrombocytopenia was evaluated by studying blood samples from 100 patients with suspected he parin-induced thrombocytopenia, and categorized into 4 clinical groups: unl ikely (n = 22), possible (34), probable (36), and definite (8) thrombocytop enia. Results of the platelet aggregation test were positive 40 of 44 patie nts with probable or definite heparin-induced thrombocytopenia (sensitivity 91%) and in 5 of 22 unlikely to have heparin-induced thrombocytopenia (spe cificity 77%). The SRA exhibited sensitivity of 88% and negative predictive value of 81%, close to those values for the platelet aggregation test; spe cificity and positive predictive value were 100%. The sensitivity of the he parin-PF4 ELISA was 97%, with specificity 86%, and a positive correlation w as recorded between the level of antibodies to H-PF4 and clinical score (P = 0.66). When ELISA was used with the platelet aggregation test or SRA, pos itive predictive value and specificity were 100% when both tests yielded po sitive results, and negative predictive value and 100% when both tests yiel ded negative results. A biologic flow chart was designed that presented ct choice based on the results of the platelet aggregation test or SRA in asso ciation with ELISIA, and enabled more accurate and specific identification of heparin-induced thrombocytopenia.