Systemic inflammatory response index in the differentiation of unstable angina pectoris and non-ST elevation myocardial infarction.

The systemic inflammatory response index (SIRI), calculated from routine complete blood count parameters, has emerged as a potential marker of inflammation and a predictor of prognosis in various cardiovascular conditions. This study aimed to evaluate the utility of SIRI in differentiating non-ST-elevation myocardial infarction (NSTEMI) from unstable angina pectoris (USAP) in patients presenting with acute chest pain. In this retrospective observational study, patients admitted to the emergency department with chest pain and subsequently diagnosed with USAP or NSTEMI were included. Only patients with negative high-sensitive troponin-I levels at the time of admission were enrolled in both groups. During follow-up, those who showed an increase in troponin levels were classified as NSTEMI, whereas patients without troponin elevation were classified as USAP. The SIRI was calculated using blood samples obtained at the time of admission to the emergency department by multiplying the neutrophil and monocyte counts and dividing by the lymphocyte count. Troponin positivity was used to distinguish NSTEMI from USAP. SIRI was assessed at admission in patients with chest pain and normal troponin. Higher SIRI levels in NSTEMI suggest its potential for early differentiation from USAP. Multivariate logistic regression analysis was performed to determine independent predictors of troponin positivity, and receiver operating characteristic curve analysis was used to assess diagnostic performance. A total of 151 patients were included in the analysis. Admission SIRI values were significantly higher in the troponin-positive (NSTEMI) group compared with the troponin-negative (USAP) group (P < .001). In multivariate analysis, higher admission SIRI levels independently predicted troponin positivity (odds ratio [OR], 1.47; 95% confidence interval [CI], 1.17-1.84; P < .001). Receiver operating characteristic analysis revealed an area under the curve of 0.71 (95% CI 0.63-0.79, P < .001). A cutoff value of 1.58 for SIRI demonstrated 72% sensitivity and 69% specificity in predicting troponin positivity. SIRI, a readily available, inexpensive, and rapidly obtainable index derived from standard complete blood count parameters, may serve as a valuable adjunctive tool for the early differentiation of NSTEMI from USAP in patients with acute chest pain. Its ease of calculation within minutes of admission makes it suitable in diverse healthcare settings.