The C-Reactive Protein/Albumin Ratio Predicts In-Hospital Mortality Across Age Groups

Background: The C-reactive protein-to-albumin (CRP/Alb) ratio integrates systemic inflammation and nutritional status and has emerged as a promising prognostic biomarker in hospitalized patients. However, because chronological age is itself a major determinant of mortality, it remains unclear whether the prognostic performance of the CRP/Alb ratio is influenced by age. Objectives: This study evaluated the prognostic performance of the CRP/Alb ratio for 30-day and 7-day in-hospital mortality, assessing the incremental contribution of chronological age and whether the association and discriminative performance of the CRP/Alb ratio differed across age groups. Methods: We retrospectively analyzed 3791 consecutive adult patients admitted to the Acute Care Unit of Clinical Medicine (formerly Internal and Aging Medicine) of the Policlinico Riuniti University Hospital, Foggia, Italy, between 2019 and 2025. The primary outcome was 30-day in-hospital mortality, whereas 7-day in-hospital mortality was considered a secondary outcome. Prognostic performance was evaluated using receiver operating characteristic (ROC) curve analysis, multivariable logistic regression, age-adjusted models, age-stratified ROC comparisons, and interaction analyses. Results: Among 3791 patients, 542 (14.3%) died within 30 days of hospitalization and 240 (6.3%) within 7 days. For 30-day mortality, the CRP/Alb ratio showed an AUC of 0.733 (95% CI 0.712-0.754), which increased to 0.759 (95% CI 0.739-0.779) after incorporating chronological age into the model (p < 0.001). For 7-day mortality, the corresponding AUCs were 0.752 (95% CI 0.724-0.781) and 0.768 (95% CI 0.740-0.796), respectively (p = 0.005). In multivariable logistic regression, each doubling of the CRP/Alb ratio was associated with higher odds of both 30-day mortality (OR = 1.484, 95% CI 1.409-1.563) and 7-day mortality (OR = 1.578, 95% CI 1.457-1.710), independently of chronological age. No significant interaction between ln(CRP/Alb ratio) and age was observed for either 30-day (p = 0.322) or 7-day mortality (p = 0.491), and age-stratified ROC curves did not differ significantly across age groups. Conclusions: The CRP/Alb ratio was independently associated with both 30-day and 7-day in-hospital mortality, with discriminative performance largely preserved across age groups. Chronological age provided a modest but statistically significant improvement in discrimination but did not significantly modify the association between the CRP/Alb ratio and mortality. These findings support the CRP/Alb ratio as a readily available marker for short-term risk stratification in hospitalized adults, while external validation is required before its use as a stand-alone clinical prediction tool.