Comparison of three different immunoassays in the diagnosis of heparin-induced thrombocytopenia.

Background: Heparin-induced thrombocytopenia (HIT) is caused by platelet activating antibodies that recognize platelet factor 4/heparin (PF4/H) complexes. Laboratory testing plays a key role in the diagnosis of HIT. As functional assays are unfeasible for most clinical laboratories, antigen binding assays are commonly used in routine testing. However, their low specificity leads to overdiagnosis of HIT. Therefore, it is advisable to improve screening tests in this setting. Methods: Blood samples from 114 patients in whom HIT was suspected were investigated using a chemiluminescence test (HemosIL (R) AcuStar HIT-IgG), a PF4/H IgG enzyme immunoassay (Lifecodes PF4 IgG), an IgG-specific lateral flow immunoassay heparin-induced thrombocytopenia (LFI-HIT, STic Expert (R) HIT) and the heparin-induced platelet aggregation (HIPA) test. Results: Twenty-nine (25.4%) out of 114 subjects with suspected HIT had a positive HIPA test. None of patients with a 4Ts score <4 were positive at HIPA. HemosIL (R) AcuStar HIT-IgG showed the best performance in term of sensitivity and specificity when used as single test. Receiver operating characteristic (ROC) analysis showed optimization of sensitivity and specificity using a cut-off of 1.13 U/mL (0.95 and 0.98, respectively). As an alternative approach, a strategy based on screening samples by STic Expert (R) HIT and then retesting positive results by Lifecodes PF4 IgG (cut-off 1 OD) or HemosIL (R) AcuStar HIT-IgG (cut-off 1.3 U/mL) showed a performance compared to a single test approach by HemosIL (R) AcuStar HIT-IgG. Conclusions: The HemosIL (R) AcuStar HIT or a combinatorial approach with the STic Expert (R) HIT and the PF4/H IgG enzyme immunoassay provide an accurate diagnosis of immune HIT.