Comparison of two PF4/heparin ELISA assays for the laboratory diagnosis ofheparin-induced thrombocytopenia

Serum samples from 105 patients with suspected heparin-induced thrombocytop enia (HIT) were evaluated using the C-14-serotonin release assay (SRA), con sidered the "gold standard" for the diagnosis of HIT, and two enzyme-linked immunosorbent assays (ELISA) that measure anti-platelet factor (PF) 4/hepa rin antibodies to determine the performance characteristics of the newly av ailable ELISA assays. Relative to the SRA, the sensitivity and specificity of the Asserachrom HPIA assay were 73% and 77%, respectively, in this popul ation of patients. The sensitivity and specificity of the GTI-HAT assay wer e 60% and 93%, respectively. In serum negative by SRA, GTI-HAT and HPIA det ected antibodies in 9% and 25%, respectively. Antibodies were detected by H PIA in 18% of the sera negative by both SRA and GTI-HAT. In a second study, samples evaluated from patients (n = 10) treated for established thrombosi s with a low-molecular-weight heparin and who had no decrease in platelet c ounts, showed a weak antibody titer in 50% of the patients after 12 days of therapy by GTI-HAT, whereas the HPIA identified a strong antibody titer in 75% of the patients after 4 days. These data suggest that the currently av ailable ELISA methods for the detection of anti-PF4/heparin antibodies offe r a limited sensitivity and specificity in comparison to SRA. The ELISA ass ays on their own are thus of limited value for the laboratory diagnosis of HIT. SRA-positive sera do not always have positive antibody titers, and ant ibodies can be present in SRA-negative sera. Furthermore, these data show t hat ELISA methods differ in their relative sensitivities and specificities for the detection of anti-PF4/heparin antibodies.