Introduction To compare 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. Diabetes was identified from hospital diagnoses, prescriptions and diabetes-specific primary care claims (17 045 MHCs, 26 626 non-MHCs). 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 20 years was higher in MHCs than in non-MHCs (9.3% vs 6.1%, p<0.001). The OR was 1.40 (95% CI 1.36 to 1.43) after controlling for sociodemographics and case mix. Receipt of recommended pathology tests (HbA_1c, microalbuminuria, blood lipids) was suboptimal in both groups, but was even lower in MHCs (at 1 year, adjusted OR, 0.81; 95% CI 0.78 to 0.85; during the entire follow-up, adjusted rate ratio (RR), 0.86, 95% CI 0.84 to 0.88; for all tests combined). MHCs also had increased risks of hospitalisation for diabetes complications (adjusted RR, 1.20, 95% CI 1.17 to 1.24), diabetes-related mortality (1.43, 1.35 to 1.52) and all-cause mortality (1.47, 1.42 to 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.