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The Manchester Acute Coronary Syndromes (MACS) decision aid can ‘rules in’ and ‘rule out’ acute coronary syndromes (ACS) by combining a patient's symptoms with the results of a single blood test taken at the time of arrival in the Emergency Department (ED). The original model (MACS) included two biomarkers: high sensitivity cardiac troponin T (hs-cTnT) and heart-type fatty acid binding protein (h-FABP). A refined model without h-FABP was found to have comparable sensitivity but greater specificity. We sought to validate MACS and T-MACS using the contemporary Siemens Advia Centaur cardiac troponin I assay to increase usability in practice.This is a secondary analysis from prospective diagnostic cohort study at Stepping Hill Hospital, United Kingdom. Patients presenting with chest pain of suspected cardiac nature warranting rule out for ACS were included. All patients underwent hs-cTnT testing at least 12 h after peak symptoms. The primary outcome was a diagnosis of ACS, defined as either prevalent acute myocardial infarction (AMI) or incident major adverse cardiac events (death, AMI or coronary revascularization) within 30 days.Of 405 included patients, 76 (18.8%) had ACS. MACS and T-MACS had similar C-statistics (0.94 for each, p = 0.36) and sensitivity (difference 1.3%, 95% CI −1.3 to 3.9%, p = 1.00) but T-MACS had significantly greater specificity (difference 16.7%, 95% CI 14.6–18.9%, p < 0.0001). T-MACS and MACS would have allowed 36.3% and 22.5% patients to be immediately discharged respectively. Of patients classified as ‘very low risk’, none had ACS when MACS was used compared to one (0.7%) with T-MACS.Both MACS and T-MACS effectively ruled out ACS even with a contemporary troponin I assay and could be used to reduce unnecessary hospital admissions.