Co-morbidity adjustment for functional outcomes in community-dwelling older adults

Objective: To characterize relationships between self-reported co-morbidity and functional outcomes in community-dwelling older adults, and to assess whether the impact of co-morbidity persists even after adjustment for baseline functional status. Design: Prospective observational study. We examined associations between self-reported co-morbidity at baseline and functional outcomes at one year, with and without adjustment for baseline functional status. Setting: Outpatient clinics at a managed care and a Veterans Affairs site. Subjects: Four hundred and fifty-seven community-dwelling older adults representing a broad spectrum of overall health status. Main outcome measures: (a) New basic ADL (activities of daily living) problem during follow-up; (b) 10-point decline in the physical function index of the MOS-36 (MOS-PFI). Results: Co-morbidity was associated with adverse functional outcomes in bivariable analyses. After adjustment for age and baseline functional status, an accumulated co-morbidity score provided additional explanatory power for predicting new ADL problems; odds ratios were 2.30 (1.09, 5.09) and 2.96 (1.48, 6.25) for 2 and ≥3 affected co-morbidity domains, respectively. The impact of baseline status was also important; odds ratios for new ADL problems were 4.77 (2.68, 8.81) when at least one instrumental activity of daily living (IADL) problem was present at baseline, and 15.6 (8.05, 31.3) when at least one basic ADL problem was present at baseline. Conclusions: Accumulated self-reported co-morbidity has significant negative effects on function at one year; these effects are attenuated but not eliminated by adjustment for baseline status. Co-morbidity adjustment is probably an important design element in clinical research focused on functional outcomes in older adults.