Prognostic value of the monocyte-to-lymphocyte ratio for adverse cardiovascular outcomes in patients with coronary artery disease: a meta-analysis of cohort studies

The monocyte-to-lymphocyte ratio (MLR) is an emerging inflammation-related biomarker that has been extensively investigated for prognostic assessment across a range of diseases. However, the prognostic value of MLR in patients with coronary artery disease (CAD) remains uncertain, particularly across populations managed with different treatment strategies. This study aimed to systematically evaluate the association between MLR and the risks of major adverse cardiovascular events (MACE) and all-cause mortality in patients with CAD, and to further assess its prognostic value among patients undergoing percutaneous coronary intervention (PCI). We systematically searched four databases-PubMed, Web of Science, Embase, and the Cochrane Library-and included retrospective or prospective cohort studies of patients with coronary artery disease, in which MACE was the primary outcome and all-cause mortality was the secondary outcome. Hazard ratios (HRs) and corresponding 95% confidence intervals (CIs) were pooled using a random-effects model. Subgroup analyses, meta-regression, and sensitivity analyses were conducted to assess the robustness of the findings and explore potential sources of heterogeneity; publication bias was evaluated using funnel plots and Egger’s test. A total of 15 cohort studies comprising 18,998 patients with CAD were included. Pooled analysis showed that higher MLR categories were significantly associated with increased risks of MACE (HR = 1.76, 95%CI 1.28–2.40; I 2 = 86.3%, P -heterogeneity < 0.0001) and all-cause mortality (HR = 1.45, 95%CI 1.21–1.73, I 2 = 36.4%; P -heterogeneity = 0.138). Subgroup analyses showed that higher MLR categories were significantly associated with an increased risk of post-procedural MACE among patients undergoing PCI (HR = 2.06, 95%CI 1.31–3.24, I 2 = 86.8%; P -heterogeneity < 0.0001), whereas this association was not statistically significant among patients who did not undergo PCI (HR = 1.42, 95%CI 0.76–2.65, I 2 = 84.6%; P -heterogeneity = 0.0002). In addition, among patients undergoing PCI, higher MLR categories were associated with an increased risk of all-cause mortality (HR = 1.34, 95%CI 1.15–1.56, I 2 = 0%; P -heterogeneity = 0.5917). However, Formal tests for subgroup differences according to PCI status were not statistically significant for MACE ( P = 0.1583) or all-cause mortality ( P = 0.4434). Sensitivity analyses indicated that the pooled estimates were robust, with no clear evidence of publication bias. Higher MLR levels were significantly associated with increased risks of MACE and all-cause mortality in patients with CAD.