Incidence of Isolated Heparin-Induced Thrombocytopenia and Risk of Thrombosis by IgG-Specific Anti-PF4/Heparin ELISA

Abstract

Heparin-induced thrombocytopenia (HIT) antibodies are screened by an enzyme-linked immunosorbent assay (ELISA). Polyspecific ELISA detects anti-PF4/heparin IgG, IgA, and IgM. Recently, anti-PF4/heparin IgG ELISA has been shown to be more specific. However, the impact of using the IgG-ELISA on the incidence of isolated HIT (thrombocytopenia alone without clinically evident thrombosis) and the risk of developing subsequent thrombosis are still unknown. A total of 492 consecutive patients with clinically suspected HIT at The University of Texas Southwestern Medical Center and affiliated hospitals were retrospectively reviewed from December 2008 to May 2010. 29 patients (6%) were diagnosed with HIT based on clinical findings and positive ELISA. 19 of the 29 patients (65%) had thrombosis at the time of diagnosis; whereas 10 of the 29 (35%) had only isolated HIT. The ten patients with isolated HIT had serial follow up for at least 3 months. 3 of 10 were treated with direct thrombin inhibitors and 5 of 10 were treated with Warfarin for at least 1 month upon discharge. None of them developed symptoms or signs of thrombosis during 3 months of follow up. The incidence of isolated HIT in this study was 35%, which is significantly lower than previously reported in the literature. It is possible that some patients previously thought to have HIT by the poly-specific ELISA assay had false positive results. The improved specificity of the IgG- ELISA appears to reduce the incidence of isolated HIT which may have lower risk of subsequent thrombosis.