AKI in Older Adults: Limitations of Chronological Age in Prognostic Indexes

Background: Acute kidney injury (AKI) increases in-hospital morbidity and mortality. Age is a recognized risk factor and is included in prognostic indices, usually as chronological age. However, this may reduce predictive accuracy in older adults, where biological and chronological age may diverge. Methods: Prospective cohort study from 1994 to 2025. Inclusion: ≥20% rise in serum creatinine. 3,274 patients were stratified by age: A (<55), B (55–64), C (65–74), D (75–84), and E (≥85). Compared the Individual Severity Index (ISI, includes age) with the Multiorgan Failure Index (MOFI, does not include age). Clinical profiles, treatment, outcomes, and health status (Karnofsky, ECOG, nutrition 0–4) were assessed. Results: Patient distribution by age group was: A (<55) 24.1%, B (55–64) 22.8%, C (65–74) 27.9%, D (75–84) 20.6%, and E (≥85) 4.6%. Overall mortality was 16.3%; by group: A 19.2%, B 19.0%, C 14.7%, D 13.0%, E 12.1%. Functional causes of AKI (mainly hypovolemia) increased with age: A 71.4%, B 75.4%, C 75.1%, D 79.7%, E 85.9%. In contrast, need for renal replacement therapy declined: A 29.4%, B 26.2%, C 26.4%, D 20.6%, E 11.4%. Chronic kidney disease rose from 26.9% in A to 71.1% in E. Inflammatory diseases were more frequent in younger patients (A 48.2%, E 31.5%). Heart failure prevalence increased from 2.7% in A to 11.4% in E. Oncologic pathology showed the opposite trend, from 40.9% in A to 6.7% in E. Mean Karnofsky declined with age: A 70.17, B 69.44, C 69.15, D 68.40, E 64.03 (p<0.001). Nutritional status (0–4 scale) decreased: A 2.16, B 2.20, C 1.98, D 2.00, E 1.77 (p<0.001). No significant differences were observed in ECOG. ISI (includes age) increased with age: A 0.259, B 0.295, C 0.310, D 0.335, E 0.336. MOFI (excludes age) decreased: A 3.83, B 3.44, C 3.24, D 2.84, E 2.42 (p<0.005). AUC for mortality prediction remained stable for MOFI but declined for ISI, with the lowest discrimination in the oldest group. Conclusion: In older adults, AKI is more often functional, with lower mortality and dialysis need. Prognostic scores based on chronological age (ISI) lose sensitivity/specificity in the elderly. Including biological age markers (frailty, functional status, nutrition) could improve prognostic precision.