Evaluation of 4T score for possible heparin induced thrombocytopenia diagnosis

Background and Objectives Heparin induced thrombocytopenia (HIT) is a prothrombotic disorder. The antibody against PF4-heparin complex may lead to platelet activation, thrombotic events and death. We decided to evaluate diagnostic value of 4T score as a clinical diagnostic system among cardiac surgery patients for diagnosis of HIT.
Materials and Methods In this descriptive study, 92 patients that underwent cardiac surgery from September 2015 till September 2016 in Tehran Modarres Hospital have been included. We evaluated 4Tscore criteria (4T stands for Thrombocytopenia, Time of thrombocytopenia, Thrombotic events and Other reasons for Thrombocytopenia) in all cases. Blood samples were obtained from patients with 4Tscore ≥ 4. Anti-platelet factor 4/heparin antibody (enzyme-immune assay, ELISA) was done for patients with 4Tscore ≥ 4 and the OD ≥ 0.2 was considered as positive and ≥1 as strong positive. Patients with 4Tscore ≥ 4 and strong positivity of ELISA test were considered as HIT.
Results From 92 patients, 67 (72.8%) were male and 25 (27.2%) female. Mean age was 58±10.68 with 14 patients (15.2%) having 4Tscore ≥ 4. ELISA was positive (OD > 0.2) in 8 cases in 3 of whom ELISA being strongly positive (OD > 1). According to HIT definition in this study, the prevalence of HIT was 3.2%.
Conclusions 4T score should be evaluated for preliminary diagnosis of HIT in suspected patients treated with heparin but the use of this system alone without laboratory confirmation can lead to over diagnosis of HIT and inappropriate termination of heparin treatment.