Prognostic Significance of the C-Reactive Protein to Albumin Ratio for Mortality in Critically Ill Adults: A Systematic Review and Meta-analysis Across Heterogeneous ICU Populations

Background Inflammation and metabolic depletion are major determinants of survival in critical illness. The C-reactive protein to albumin ratio (CAR) integrates these two physiologic domains and has emerged as a promising prognostic biomarker. Objective To evaluate the association between CAR and mortality in critically ill adult patients through a systematic review and meta-analysis. Methods We searched six databases (2015–2025) for observational studies reporting CAR and mortality. Two reviewers screened articles, extracted data, and assessed quality using the Newcastle–Ottawa Scale. Random-effects models (DerSimonian–Laird, Hartung-Knapp-Sidik-Jonkman, and REML) were applied separately for odds ratios (OR) and hazard ratios (HR). Meta-regression explored sources of heterogeneity. Results Eleven studies were included. Elevated CAR was associated with increased mortality (OR 1.85, 95% CI 1.23–2.78; HR 1.10, 95% CI 1.06–1.14). Heterogeneity was high (I² ≈ 90%). Meta-regression identified age, albumin, diabetes burden, and severity of illness as significant modifiers. Sensitivity analyses confirmed effect robustness. No publication bias was detected. Conclusion Elevated CAR is consistently associated with higher mortality in critically ill adults. Its accessibility and biological plausibility support CAR as a clinically useful adjunct for early risk stratification.