Chronic conditions and mortality among the oldest old

Objectives. We sought to determine whether chronic conditions and functional limitations are equally predictive of mortality among older adults.Methods. Participants in the 1998 wave of the Health and Retirement Study (N=19430) were divided into groups by decades of age, and their vital status in 2004 was determined. We used multivariate Cox regression to determine the ability of chronic conditions and functional limitations to predict mortality.Results. As age increased, the ability of chronic conditions to predict mortality declined rapidly, whereas the ability of functional limitations to predict mortality declined more slowly. In younger participants (aged 50–59 years), chronic conditions were stronger predictors of death than were functional limitations (Harrell C statistic 0.78 vs. 0.73; P=.001). In older participants (aged 90–99 years), functional limitations were stronger predictors of death than were chronic conditions (Harrell C statistic 0.67 vs. 0.61; P=.004).Conclusions. The importance of chronic conditions as a predictor of death declined rapidly with increasing age. Therefore, risk-adjustment models that only consider comorbidities when comparing mortality rates across providers may be inadequate for adults older than 80 years.Numerous studies have shown that both chronic conditions and functional limitations are powerful independent predictors of mortality.1^–4 However, a growing body of research suggests that some risk factors behave differently in people at different ages.5^–10 Some researchers have found that well-established mortality risk factors among younger persons, such as hypertension,7^,8^,11 hypercholesterolemia,7^,8^,12 increased body mass index,7^,9^,13^,14 heart disease,5^,8^,9 and cancer,5^,9 may not continue to pose a risk to the oldest old, suggesting that the association between chronic conditions and mortality may be weaker in the elderly. Autopsy series have also supported this notion, showing that a definitive cause of death attributable to a single disease process is often not found among older people.15 These observations have spurred a growing recognition within the geriatrics community that our methods of measuring and accounting for the burden of disease may be inappropriate for our oldest patients.16^–18Despite these concerns, chronic disease diagnoses remain at the center of clinical care and risk adjustment for older patients.17 However, if the association between chronic conditions and mortality is weaker in the elderly, risk adjustment tools that rely solely on chronic disease diagnoses (such as the Charlson Comorbidity Index19 and the Elixhauser method20) may be suboptimal for our oldest old. Therefore, the use of these methods to compare risk-adjusted outcomes as a proxy for the quality of care21^,22 may lead to erroneous conclusions. Improved risk-adjustment methods may lead to improvements in targeting health care quality interventions, ultimately resulting in better population health outcomes.To address these issues, we examined the ability of specific types of risk factors—chronic conditions, functional limitations, and demographic variables—to differentiate between people at high and low risk of death across a range of age groups. Based on previous research, we hypothesized that chronic conditions would be less predictive of death among older people. Because functional limitations often represent a final common pathway of decline regardless of underlying etiology,23^–25 we further hypothesized that functional limitations would be a stronger predictor of mortality than chronic conditions among our oldest participants.