Implementation of Whole-Blood Impedance Aggregometry for Heparin-Induced Thrombocytopenia Functional Assay and Case Discussion

OBJECTIVES: The diagnosis of heparin-induced thrombocytopenia (HIT) ideally requires a functional assay to confirm. 14C-serotonin release assay (SRA) as "gold standard" is technically challenging and unsuitable for routine use. We conducted a study to assess the performance of whole-blood impedance aggregometry (WBIA) as a simple and rapid HIT functional assay. METHODS: Platelet factor 4 (PF4)/immunoglobulin G (IgG) antibody, WBIA, and SRA were tested on 70 patients suspected of having HIT. Patients with a 4Ts score of 4 or more, positive PF4/IgG, and positive SRA were considered HIT positive; others were designated HIT negative. RESULTS: WBIA had 85.7% (6/7) sensitivity and 98.4% (61/62) specificity, which were not statistically different compared with SRA. Sixty-two of 70 patients had concordant results (five positive and 57 negative) by both WBIA and SRA. Eight discordant cases revealed the importance of recognizing donor effect, interferences, and the presence of heparin-independent or non-heparin-dependent antibodies in functional assays. CONCLUSIONS: Implementation of WBIA could facilitate timely diagnosis and management of HIT.