Mental illness related disparities in diabetes prevalence, quality of care and outcomes: A population-based longitudinal study

Background/Objective: Previous studies suggest that mental illness is associated with disparities in physical health outcomes and physical health care. To test these, we compared the prevalence of diabetes, quality of care and outcomes between mental health clients (MHCs) and non-MHCs. Methods: Population-based longitudinal study of 139,208 MHCs and 294,180 matched non-MHCs in Western Australia (WA) from 1990 to 2006, using linked data of WA State mental health registry, electoral roll registrations, hospital admissions, emergency department attendances, deaths, and Commonwealth Medicare and pharmaceutical benefits claims. We used the electoral roll as the sampling frame for both cohorts to enhance internal validity of the study and the mental health registry to separate MHCs from non-MHCs. Non-MHCs were matched 2:1 with MHCs by 5-year age group, sex and current electoral roll registration at study entry. Diabetes was identified from hospital diagnoses, prescriptions and diabetes-specific primary care claims (17,045 MHCs, 26,626 non-MHCs). Main outcome measures were prevalence of diabetes; likelihood of receiving recommended pathology tests for ongoing diabetes monitoring; risks of hospitalisation for diabetes complications, diabetes-related mortality and all-cause mortality. Results: Age-sex-standardised point-prevalence of diabetes in those aged „d20 years was higher in MHCs than in non-MHCs (9.3% vs 6.1%, p<0.001). The odds ratio (OR) was 1.40 (95% CI, 1.36-1.43) after controlling for sociodemographics and case mix. Receipt of recommended pathology tests (HbA1c, microalbuminuria, blood lipids) was suboptimal in both groups, but was even lower in MHCs (at one year, adjusted OR, 0.81; 95% CI, 0.78-0.85; during the entire follow-up, adjusted rate ratio (RR), 0.86, 95% CI 0.84-0.88; for all tests combined). MHCs also had increased risks of hospitalisation for diabetes complications (adjusted RR, 1.20, 95% CI 1.17-1.24), diabetes-related mortality (1.43, 1.35-1.52) and all-cause mortality (1.47, 1.42-1.53). The disparities were most marked for alcohol/drug disorders, schizophrenia, affective disorders, other psychoses and personality disorders. Conclusion: MHCs require improved prevention and control of diabetes, especially at the primary care level.