Association of a Low Eosinophil-to-Monocyte Ratio With One-Month All-Cause Mortality in Patients With ST-Segment Elevation Myocardial Infarction: A Cohort Study.

Introduction ST-elevation myocardial infarction (STEMI) remains a major driver of premature cardiovascular death across South Asia, where many hospitals must triage patients without routine access to advanced risk-stratification tools. The eosinophil-to-monocyte ratio (EMR), derived at no added cost from the complete blood count (CBC) every STEMI patient already receives, has been proposed as a low-cost prognostic marker. This study examined whether EMR at admission is independently associated with one-month all-cause mortality among STEMI patients in Pakistan. Methods This prospective cohort study enrolled 226 patients aged 18-50 years with confirmed STEMI at the Emergency Department of the Punjab Institute of Cardiology, Lahore, Pakistan, from August 20, 2020, to February 20, 2024: 113 with a low admission EMR (<0.18) and 113 without (≥0.18). Patients were followed for one month for all-cause mortality, and independent predictors of mortality were identified using multivariate logistic regression adjusted for age, sex, hypertension, diabetes, smoking, and previous myocardial infarction. Results Among the 226 patients followed for 30 days, those with a low EMR died at more than three times the rate of those without (9.7% versus 2.7%, p = 0.027), and low EMR remained an independent predictor of death after adjustment for traditional risk factors using Firth's penalized logistic regression (adjusted odds ratio (AOR) 3.89, 95% confidence interval (CI) 1.21-13.84, p=0.025). Conclusion In this cohort of STEMI patients, a low EMR at admission was independently associated with significantly increased mortality at one month (AOR 3.89; 95% CI 1.21-13.84; Firth's penalized logistic regression). Because the confidence interval is wide and the number of deaths is small, these results are hypothesis-generating, and a larger multi-center, external validation study is required before EMR can be recommended for STEMI triage protocols. If these results are replicated, the benefits of implementing EMR could be compelling for risk stratification in health systems where cutting-edge diagnostics are not widely adopted due to its close-to-zero marginal cost.