Admission creatinine and outcomes in very elderly critically ill patients: a retrospective cohort study

Serum creatinine at ICU admission is a central component of prognostic assessment in critically ill patients and is widely used as a marker of kidney function in clinical practice, as well as being incorporated into established prediction models. However, in very old patients, age-related muscle loss, frailty, and altered creatinine kinetics may limit its validity. With ICU admissions among nonagenarians (≥ 90 years) steadily increasing, it remains unclear whether admission creatinine retains its prognostic relevance in this population. We therefore evaluated the prognostic value of admission creatinine for short- and long-term outcomes in critically ill nonagenarians and assessed its role within the SOFA score.

This retrospective cohort study included all patients aged ≥ 90 years admitted to the ICUs of the University Medical Center Hamburg-Eppendorf between 2008-2019. Admission serum creatinine was analyzed as the primary exposure variable. Primary outcomes were in-hospital, 90-day, and 1-year mortality. Associations between admission creatinine and outcomes were analyzed using logistic and Cox regression models adjusted for relevant confounders. To evaluate the prognostic contribution of kidney function to established risk scores, we compared the predictive performance of the full SOFA score with a modified SOFA score excluding the kidney (creatinine) component.

Among 952 patients (median age 92.2 years) in-hospital, 90-day, and 1-year mortality rates were 28.5%, 42.2%, and 57.1%, respectively. Admission creatinine was not independently associated with in-hospital mortality (adjusted hazard ratio [HR] 1.07, 95% CI 0.92-1.26). In contrast, higher admission creatinine independently predicted 90-day mortality (adjusted HR 1.16, 95% CI 1.01-1.34) and 1-year mortality (adjusted HR 1.20, 95% CI 1.06-1.36). The Full and non-kidney SOFA scores performed similarly (AUC 0.79 each).

In critically ill patients aged ≥ 90 years, admission creatinine does not independently predict short-term outcomes but remains a robust predictor of mid- and long-term mortality. The unchanged performance of the SOFA score after removal of its kidney component underscores the limited relevance of creatinine for short-term risk stratification in this age group and supports age-adapted interpretation of kidney biomarkers and prognostic models in very old ICU patients.