Beyond comorbidity: expanding the definition and measurement of complexity among older adults using administrative claims data.

BACKGROUND: Studies of patients with multiple chronic conditions using claims data are often missing important determinants of treatments and outcomes, such as function status and disease severity. We sought to identify and evaluate a class of function-related indicators (FRIs) from administrative claims data.

POPULATION: The study cohort comprised US Medicare beneficiaries aged 65 years or older with Parts A and B fee-for-service and Part D coverage, with a hospitalization for acute myocardial infarction during 2007.

METHODS: Measures during the year before admission included the FRIs, demographics, conventional comorbidity measures, and prior hospitalization. Outcomes were receipt of cardiac catheterization during the index hospitalization and 12-month mortality. Model development used a random sample (n=72,056) with an equal sample for validation.

RESULTS: In addition to prior cardiovascular conditions (85%), 40% had ≥1 comorbid condition, 30% were hospitalized in the prior 6 months, and 65% had ≥1 FRI [eg, delirium/dementia (22.7%), depression (16.7%), mobility limitation (16.1%), and chronic skin ulcers (12.6%)]. Including the FRIs improved mortality and cardiac catheterization prediction models (C-statistics 0.71 and 0.77, respectively). Patients with more cardiovascular conditions received less cardiac catheterization [minimally adjusted odds ratio (OR) 0.83; 95% confidence interval (CI), 0.82-0.83], as did patients with more comorbidities (minimally adjusted OR 0.70; 95% CI, 0.69-0.71), but this was attenuated by adjusting for functional status (fully adjusted OR for cardiovascular conditions 0.95; 95% CI, 0.94-0.96 and for comorbid conditions 0.94; 95% CI, 0.92-0.95).

CONCLUSIONS: Claims data studies that include indicators of potentially diminished patient functional status better capture heterogeneity of patients with multiple chronic conditions.