OBJECTIVE To evaluate the relationship between diabetes care and types of comorbidity, classified by the degree to which their treatment is concordant with that for diabetes.

RESEARCH DESIGN AND METHODS Retrospective cohort study (fiscal year [FY] 2001 to FY 2004) of 42,826 veterans with new-onset diabetes in FY 2003. Veterans were classified into five chronic comorbid illness groups (CCIGs): none, concordant only, discordant only, both concordant and discordant, and dominant. Five diabetes-related care measures were assessed in FY 2004 (guideline-consistent testing and treatment goals for HbA_1c and LDL cholesterol and diabetes-related outpatient visits). Analyses included logistic regressions adjusting for age, race, sex, marital status, priority code, and interaction between CCIGs and visit frequency.

RESULTS Only 20% of patients had no comorbidities. Mean number of visits per year ranged from 7.8 (no CCIG) to 17.5 (dominant CCIG). In unadjusted analyses, presence of any illness was associated with equivalent or better care. In the fully adjusted model, we found interaction between CCIG and visit frequency. When visits were <7 per year, the odds of meeting the goal of HbA_1c <8% were similar in the concordant (odds ratio 0.96 [95% CI 0.83–1.11]) and lower in the discordant (0.90 [0.81–0.99]) groups compared with the no comorbidity group. Among patients with >24 visits per year, these odds were insignificant. Dominant CCIG was associated with substantially reduced care for glycemic control for all visit categories and for lipid management at all but the highest visit category.

CONCLUSIONS Our study indicates that diabetes care varies by types of comorbidity. Concordant illnesses result in similar or better care, regardless of visit frequency. Discordant illnesses are associated with diminished care: an effect that decreases as visit frequency increases.