Establishing a Gradient of Risk in Patients with Acute Coronary Syndromes Using Troponin I Measurements

Abstract

Objective: To evaluate the role of serum troponin I (TnI) estimations in the early risk stratification of patients with acute coronary syndromes (ACS) subsequently diagnosed as acute myocardial infarction (AMI) or unstable angina (UA). Subjects and Methods: Blood samples were collected from 86 patients admitted to the Coronary Care Unit of the Mubarak Al-Kabeer Hospital, Kuwait, with a diagnosis of ACS on admission (TnI-1) and after 8 h (TnI-2) and 16 h (TnI-3). Blood was also collected from 38 age-matched healthy controls for comparison. Serum TnI was measured by paramagnetic particle chemiluminescent immunoassay. Results: Serum TnI of <0.05 ng/ml, corresponding to the 99th percentile, was established for healthy subjects. Patients diagnosed as UA had a 99th percentile TnI-1 value of about 0.30 ng/ml. The best specificity and sensitivity for ACS was obtained for TnI-2; indeed, TnI-2 >0.3 ng/ml gave a >80% certainty of diagnosis of AMI. Also, TnI-2 <0.3 ng/ml in ACS patients was approximately 80% sensitive for the diagnosis of UA but relatively nonspecific (approximately 40%). Specificity for TnI-2 for the diagnosis of UA improved to about 90% by narrowing the diagnostic range to 0.05–0.3 ng/ ml. TnI values in UA increased by <100% at 8 h, while in AMI, this increase was up to 1,000%. Conclusion: In the evaluation of ACS, admission and 8-hour serum TnI <0.05 ng/ml is probably not cardiac in origin; serum TnI >0.3 ng/ml on admission and increasing rapidly by 8 h is likely AMI, and serum TnI >0.05 and <0.3 ng/ml on admission with a mild increase by 8 h is likely due to UA.