Diagnosis of myocardial infarction in early presenters using 1-hour delta of high sensitive Troponin I: a pilot study.

BACKGROUND: The accurate and timely diagnosis of Non-ST Elevation Myocardial Infarction (NSTEMI) in early presenter is important to reduce false negative cases. We aimed to discern the diagnostic cut-off of high-sensitive cardiac Troponin I (hs-cTnI) in early presenters who lack preexisting cardiac morbidity. METHOD: This is a record-based study in which we included data from 457 patients who presented to emergency care with symptoms suggestive of suspected Acute Coronary Syndrome (ACS). We calculated sensitivity and Negative Predictive Value (NPV) for rule out and specificity and Positive Predictive Value (PPV) to rule in NSTEMI at various cut-off levels of hs-cTnI. In addition, we used binary logistic regression to identify the best predictor for NSTEMI diagnosis. RESULT: We observed 91% sensitivity and 79% NPV at a baseline hs-cTnI level below 2 ng/L. However, this was insufficient to rule out NSTEMI. In addition, we found 1-hour delta (absolute delta) hs-cTnI to be the best predictor of NSTEMI. To rule in NSTEMI, specificity was 95%, and PPV was 77% at 4 ng/L 1-hour delta hs-cTnI. The Area Under Curve (AUC) in the Receiver Operating Characteristic (ROC) was 0.796 (p-value = 0.001) for 1-hour delta hs-cTnI. CONCLUSION: In early presenters without prior heart disease, a single baseline hs-cTnI measurement below 3 ng/L provided 86% NPV, but this was insufficient for safe rule-out, confirming that serial sampling is necessary. Standard 99th percentile cut-offs performed poorly in this population. Incorporation of a 1-hour delta assessment improved diagnostic discrimination. Further, even a low 1-hour delta hs-cTnI (4 ng/L) can rule in NSTEMI. However, due to nature of this pilot study, our 4 ng/L rule-in criterion needs to be validated in further studies before being used in the clinics.