Background: Heparin-induced thrombocytopenia (HIT) should be diagnosed clinically as well as by laboratory assays for timely recognition, prevention and management of complications. Objective: To evaluate the clinical utility of pre-test clinical scoring system in combination with two immunoassays for the diagnosis of HIT in cardiac surgery patients. Materials and methods: A total of 100 consecutive patients undergoing cardiac surgery were studied. Pre-test clinical scoring was carried out in patients with thrombocytopenia and further tested by two immunoassays, i.e. Heparin platelet factor 4 (H-PF4) enzyme-linked immunosorbent assay (ELISA) and particle gel immunoassay (PaGIA). Results: Of the 100 patients studied, 42 patients developed thrombocytopenia post-operatively. On pre-test clinical scoring, low T-score was observed in 6 patients, intermediate in 28 and high score in 8 patients, whereas 19 patients (45·2%) were positive by H-PF4 ELISA and 10 (23·8%) by PaGIA for H-PF4 antibody. The difference in the incidence of clinically significant HIT antibodies in the three categories was statistically significant. A good correlation was also observed with ELISA optical density, T-scoring and PaGIA. Conclusions: Pre-test clinical scoring correlates well with the development of H-PF4 antibodies which are incriminated in the causation of thrombotic complications in patients with HIT. We also propose a protocol for diagnosing patients with clinical suspicion of HIT using pre-test clinical scoring and immunoassay.