Contributions of biological tests and the 4 Ts score in the diagnosis of Heparin Induced Thrombocytopenia

INTRODUCTION: Heparin-induced thrombocytopenia (HIT) is an adverse drug reaction caused by antibodies to the heparin/platelet factor 4 (PF4) complexes. HIT diagnosis is challenging and depends on clinical presentation and laboratory tests. We investigated the interest of the combined use of 4 Ts score and the functional and immunological tests for the diagnosis of HIT. METHODS: We analyzed 178 patients with suspected HIT, for which the 4 Ts score was calculated. Heparin-PF4 antibodies were detected by both Heparin-induced platelet activation test (HIPA) and Heparin platelet induced antibodies enzyme immunoassay. RESULTS: Our results shown that in low probability group, 85% of plasmas were found negative versus 55.5% in the high probability group. On the other hand, 22.2% of patients were HIT positive in high probability group versus 0% in the low probability group. CONCLUSION: These results confirmed that the negative predictive value of the HIT score was high. The 4T's model has demonstrated excellent sensitivity but its specificity was limited. The specificity of the functional and immunological test is high only in a context suggestive of HIT. Both methods should be considered complementary in the diagnostic strategy.