Establishing a gradient of risk in patients with acute coronary syndromes using troponin I measurements.

OBJECTIVE

To evaluate the role of serum troponin I (Tnl) 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 (Tnl-1) and after 8 h (Tnl-2) and 16 h (Tnl-3). Blood was also collected from 38 age-matched healthy controls for comparison. Serum Tnl was measured by paramagnetic particle chemiluminescent immunoassay.

RESULTS

Serum Tnl of < 0.05 ng/ml, corresponding to the 99th percentile, was established for healthy subjects. Patients diagnosed as UA had a 99th percentile Tnl-1 value of about 0.30 ng/ml. The best specificity and sensitivity for ACS was obtained for Tnl-2; indeed, Tnl-2 > 0.3 ng/ml gave a > 80% certainty of diagnosis of AMI. Also, Tnl-2 < 0.3 ng/ml in ACS patients was approximately 80% sensitive for the diagnosis of UA but relatively nonspecific (approximately 40%). Specificity for Tnl-2 for the diagnosis of UA improved to about 90% by narrowing the diagnostic range to 0.05-0.3 ng/ml. Tnl 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 Tnl < 0.05 ng/ml is probably not cardiac in origin; serum Tnl > 0.3 ng/ml on admission and increasing rapidly by 8 h is likely AMI, and serum Tnl > 0.05 and < 0.3 ng/ml on admission with a mild increase by 8 h is likely due to UA.