The interaction between age and comorbidity contributes to predicting the mortality of geriatric patients in the acute‐care hospital

Incalzi RA, Capparella O, Gemma A, Landi F, Bruno E, Di Meo F, Carbonin P (Instituto di Medicina Interna e Geriatria dell'Universita' Cattolica del Sacro Cuore, Rome, and the Teaching Nursing Home ‘Cittadella della Carita’, Taranto, Italy. The interaction between age and comorbidity contributes to predicting the mortality of geriatric patients in the acute‐care hospital. J Intern Med 1997; 242 : 291–8. Objective To test the predictive power of comorbidity and of the interaction between age and comorbidity in geriatric patients with acute medical illness. Design Prospective observational study. Setting Medical and geriatric wards of an acute‐care hospital. Subjects Three hundred and seventy patients over 70 years of age consecutively admitted in an 18‐month period. Main outcome measure In‐hospital mortality. Method On admission a multidimensional assessment was performed, and a comorbidity index and an age–comorbidity index developed on a comparable training population were calculated. The comorbidity index is based upon a scoring system that quantifies the prognostic weight of individual diseases, while the age–comorbidity index corrects the former for the age‐related increase of the risk of death. The predictive power of variables univariately correlated with the outcome was tested by logistic regression. Results Death was independently predicted by clinical diagnosis of malnutrition (odds ratio = 1.87, confidence limits CL = 1.20–2.86), age–comorbidity index > 7 (odds ratio = 1.77, CL = 1.15–2.72), preadmission impairment in activities of daily living (odds ratio = 1.74, CL = 1.13–2.69), lymphocytopenia (odds ratio = 1.74, CL = 1.15–2.61). A weaker predictive model was obtained by substituting the comorbidity index for the index of age–comorbidity. Excluding comorbidity from the logistic regression greatly weakened the predictive model.