We prospectively evaluated the diagnostic accuracy of a new rapid assay (STic Expert HIT) alone or in combination with a clinical score in 90 HIT-suspected patients. The 4Ts score was calculated, and ELISA and serotonin-release assay (SRA) were performed; the average time taken for test results were 2 and 5 days for ELISA and SRA, respectively. The STic test was performed in our laboratory as an evaluation exercise and the result was available in 1 hour, but results were not communicated to the clinicians so as to not influence management. Diagnostic performance of STic test was assessed, alone and in combination with 4Ts score. HIT was diagnosed in 19 patients. The sensitivity, specificity, and positive and negative predictive values for the STic test alone were 95%, 92%, 75%, and 98%, respectively, with an accuracy of 92%. The likelihood ratio for positive and negative results with the STic test was 11.2 and 0.06. The combination of the 4Ts score and the STic test results had a negative predictive value of 100% and a negative likelihood ratio of 0. The favorable performance of the STic test may allow for the rapid exclusion of HIT in combination with a low to intermediate pretest clinical probability. During the subsequent year, using the STic test in real time to rapidly exclude the diagnosis, we observed a 50% reduction in danaparoid administration in HIT-suspected patients.