Heparin-induced thrombocytopenia (HIT) is a serious immunological complication of heparin administration. Diagnosis of HIT is challenging, especially in critically ill patients. The clinical scoring model for predicting HIT is helpful for guiding clinical decision. We analysed data of patients who underwent the heparin-induced platelet aggregation (HPA) test from 2006 to 2010 and compared diagnostic performance of the novel model HIT expert probability (‘HEP’), which has been validated in a population mainly comprising surgical patients first, by the previously published model ‘4Ts’ score. Clinical courses of the patients were also reviewed to ensure that HPA test results were accurate. There were 47 suspected HIT patients. The majority was from medical (70.2%) and/or critical care (61.7%) units. Ten (21.3%) yielded positive HPA. Among positive HPA patients, eight were medical patients. The HEP score ranged from −3 to 13, whereas the 4Ts score ranged from 3 to 7 in positive HPA patients. Both HEP and 4Ts scores were significantly higher in positive HPA than in negative HPA patients (5.35 vs. 1.81, P = 0.010 and 4.85 vs. 3.32, P = 0.001, respectively). The HEP score did not display better diagnostic performance than the 4Ts score, with receiver operating characteristic (ROC) area under curve of 0.72 and 0.79 (P = 0.31), respectively. The HEP score did not show better diagnostic performance than the 4Ts score for predicting HIT in our population. A large prospective validation in different sets of patients is warranted.