Laboratory diagnosis of heparin‐induced thrombocytopenia: A retrospective experience

Background Heparin‐induced thrombocytopenia (HIT) is a severe complication of heparin therapy associated with thrombosis that requires a quick diagnosis. Therefore, laboratory assays must provide an accurate and swift answer. This work aims to evaluate the performances of an ELISA assay, especially when combined with 4T risk score, and a functional assay. Methods Data were collected for 894 patients treated by heparin who underwent anticoagulant switch because of HIT suspicion and were examined by a multidisciplinary expert team who confirmed or ruled out HIT diagnosis. All patients were tested for anti‐PF4 IgG with Asserachrom HPIA IgG (ELISA), and 307 were tested with a platelet aggregation test done on platelet‐rich plasma (PRP‐PAT). The 4T risk score was available for 607 of them. Results HIT was diagnosed in 232 patients. 4T risk score had a 94.2% negative predictive value (NPV) for risk scores ≤3 and 77.3% for risk scores ≤5. The sensitivity of ELISA was 90.9%, its specificity 79.0%, and its NPV 96.1%. When combined with 4T risk score, its NPV reached 100% and 97% for risk scores ≤3 and ≤5, respectively. PRP‐PAT sensitivity was 70.4%, and its specificity was 92.3%. Combination of ELISA and PRP‐PAT had a 0.7% false‐negative rate. Conclusion This study shows that ELISA can rule out HIT with an excellent NPV, especially when combined with the 4T risk score. Nonetheless, it has low specificity; hence, it needs to be associated with a functional assay. Heparin‐induced thrombocytopenia (HIT) is life‐threatening and requires an accurate diagnosis. Therefore, data were examined for 894 patients to determine the performances of laboratory diagnosis of HIT. ELISA had an excellent negative predictive value for low and intermediate (100% and 97.0%) 4T risk scores and the functional assay had a 70.4% sensitivity and 92.7% specificity. These findings support the combination of ELISA and functional assay, with a 0.7% false‐negative rate.