Validity of ICU prognostic risk stratification tools in the oldest patients: a comparative analysis of clinical scores in a multicenter binational cohort

Abstract

Background: With the growing numbers of nonagenarians and centenarians admitted to intensive care, clinicians face complex decisions regarding care appropriateness and intensity. Prognostic tools such as APACHE III, SOFA, and the Australia and New Zealand Risk of Death (ANZROD) model are widely used, yet their validity in very old patients remains uncertain given the influence of frailty, multimorbidity, and age-related physiological changes. In this study, we evaluated and compared the performance of APACHE III, its Risk of Death score, SOFA, and ANZROD in a large binational cohort of ICU-admitted nonagenarians and centenarians, assessing discrimination, calibration, and predictive utility for short- and long-term mortality using AUROC, standardized mortality ratios, and decision curve analysis. Methods: We conducted a multicenter retrospective cohort study of 40,910 patients aged 90 years and older who were admitted to ICUs across Australia and New Zealand from 2010 to 2024. Discrimination was assessed using time-dependent area under the receiver operating characteristic curve (AUROC). Calibration was evaluated with standardized mortality ratios (SMRs), and clinical utility was examined using decision curve analysis (DCA) across ICU, hospital, 1-month, 6-month, and 1-year mortality outcomes. Results: ANZROD consistently showed the highest discriminative ability, with AUROCs of 0.870 for ICU mortality and 0.768 for 1-month mortality. APACHEIII ROD and APACHE III followed, while SOFA had the lowest AUROCs across all timepoints. SMR analysis revealed overestimation of short term and underestimation of long term mortality by all models. ANZROD had the best calibration for hospital mortality. DCA showed ANZROD provided greater net benefit than the other scores at clinically relevant thresholds. Conclusions: In this large binational cohort of over 40,000 nonagenarian and centenarian ICU patients, ANZROD outperformed APACHE III and SOFA in short-term mortality prediction, but all models showed poor calibration and declining discrimination over longer horizons. Current scores remain useful for benchmarking but are limited for individual decision-making, underscoring the need for age-specific prognostic tools that integrate frailty, function, and geriatric priorities. Trial registration: ACTRN12625000775415 (23/07/2025).