Agreement between drug treatment data and a discharge diagnosis of diabetes mellitus in the elderly

The authors examined agreement between drug treatment data and a discharge diagnosis of diabetes, considered whether agreement was modified by demogra phic variables and measures of comorbidity, and evaluated construct validit y through consideration of relations with subsequent mortality. The study s ample comprised 81,700 residents of New Jersey aged 65-99 years who had pre scription drug coverage either through Medicaid or that state's Pharmacy As sistance for the Aged and Disabled program and had at least one hospitaliza tion between July 1, 1989, and June 30, 1991. In this population, 16.4% fil led a prescription for insulin or an oral hypoglycemic agent during the 120 days before admission, and 16.3% had a discharge diagnosis of diabetes. Ov erall agreement between these two indicators was modest (kappa = 0.67, 95% confidence interval 0.66-0.67) and was weaker in those aged 85 years and ab ove (kappa = 0.58, 95% confidence interval 0.56-0.60), those in nursing hom es (kappa = 0.42, 95% confidence interval 0.39-0.44), and those with a high level of comorbidity (modified Charlson index greater than or equal to 5; kappa = 0.59, 95% confidence interval 0.56-0.62). Presence of a diagnosis o f diabetes was associated with an apparent 24% reduction in the risk of dea th during the study interval (p < 0.001), while prior treatment for diabete s had little relation to mortality (p = 0.15). These paradoxical associatio ns with mortality and the lower agreement between discharge diagnoses and d rug treatments associated with older age, nursing home residence, and comor bidity suggest limitations in the use of claims data to identify diabetes i n the elderly.