[Comorbidity in the elderly: utility and validity of assessment tools].

Comorbidity is common in the elderly and contributes to the complexity of this population subgroup. This problem is a risk factor for major adverse events such as functional decline, disability, dependency, poor quality-of-life, institutionalization, hospitalization and death, but is not the most important factor. Age and risk of functional decline rather than comorbidity (understood as a compilation of diseases) are the main characteristics defining the target population attended by geriatricians. Comorbidity indexes should not be interpreted independently in the elderly, but within a context of comprehensive geriatric assessment that includes age-related preclinical dysfunctions, frailty measures, and functional, mental and psychosocial issues. The clinical management of comorbidity in the elderly requires advanced knowledge of geriatrics because the treatment of one condition may worsen or lead to the development of others and because preclinical physiological dysfunctions modulate drug response. Recommending a specific comorbidity index is difficult and depends on multiple factors, due to their psychometric characteristics, applicability in the elderly and their construct. However, the Cumulative Illness Rating Scale, in the version adapted to the elderly, could be highly suitable. Other instruments, such as the Charlson index, the Index of CoExistent Disease and the Kaplan index are also valid and reproducible.