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

Abstract

Background: Health care disparity is a public health challenge. We compared the prevalence of diabetes, quality of care and outcomes between mental health clients (MHCs) and non-MHCs.

Methods: This was a 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 mental health registry, electoral roll registrations, hospital admissions, emergency department attendances, deaths, and 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). Both univariate and multivariate analyses adjusted for socio-demographic factors and case mix were performed to compare the outcome measures among MHCs, category of mental disorders and non-MHCs.

Results: The prevalence of diabetes was significantly higher in MHCs than in non-MHCs (crude age-sex-standardised point-prevalence of diabetes on 30 June 2006 in those aged ≥20 years, 9.3% vs 6.1%, respectively, P < 0.001; adjusted odds ratio (OR) 1.40, 95% CI 1.36 to 1.43). Receipt of recommended pathology tests (HbA1c, microalbuminuria, blood lipids) was suboptimal in both groups, but was lower in MHCs (for all tests combined; adjusted OR 0.81, 95% CI 0.78 to 0.85, at one year; and adjusted rate ratio (RR) 0.86, 95% CI 0.84 to 0.88, during the study period). 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.

Conclusions: MHCs warrant special attention for primary and secondary prevention of diabetes, especially at the primary care level.

Figure 1

Selection of study cohorts from the Western Australia Data Linkage System. Abbreviations: ED, emergency department data; ER, electoral roll registrations; MBS, Medicare Benefits Scheme data; MHCs, mental health clients; MHR, mental health registry; non-MHC, non-mental health clients; PBS, Pharmaceutical Benefits Scheme data; WADLS, the Western Australian Data Linkage System. * Patients who had contact with a community mental health service, but for whom clinicians provided no further information on the number of service contacts. These could be referrals, once-only visits or situations in which health services were not compliant in providing service contact data.

Figure 2

Point prevalence of diabetic MHCs and non-MHCs on 30 June 2006. Abbreviations: MHCs, mental health clients; MH Dx, mental health diagnosis; MHR, mental health registry.

Figure 3

Multivariate logistic regression for diabetes prevalence and receipt of pathology tests for routine diabetes monitoring at one year of follow-up. Abbreviations: MH Dx, mental health diagnosis; MHR, mental health registry; non-MHCs, non-mental health clients. Multivariate logistic regression model of diabetes prevalence adjusted for five-year age group; sex; Indigenous status; level of social disadvantage; level of residential remoteness and physical comorbidities. Multivariate logistic regression model of cumulative incidence of pathology test at one year adjusted for five-year age group, sex, Indigenous status, level of social disadvantage, level of residential remoteness, physical comorbidities, calendar year and whether diabetes was identified before T₀ and type of diabetic treatment. The reference group was non-MHCs.

Figure 4

Multivariate regression for first hospitalisation for diabetes complications, diabetes-related mortality and all-cause mortality. Abbreviations: MH Dx, mental health diagnosis; MHR, mental health registry; non-MHCs, non-mental health clients. Multivariate models adjusted for five-year age group, sex, Indigenous status, level of social disadvantage, level of residential remoteness, physical comorbidities, calendar year, whether diabetes was identified before T₀ and type of diabetes treatment. The reference group was non-MHCs.