Diabetes monitoring and control in diabetic patients with and without severe mental illness using the Clinical Practice Research Datalink (CPRD)

Problem

People with severe mental illness (SMI) are at an increased risk of developing physical health conditions, including diabetes, and have a significantly shorter life expectancy than the general population. People with SMI and comorbid diabetes are a growing population, and have poorer outcomes compared to adults with diabetes but no SMI. It has been suggested that this disparity could in part be explained by poorer diabetes monitoring and control in the SMI population. The objective was to describe and compare diabetes monitoring and control in diabetes patients with and without diagnosed SMI.

Approach

Interrogation of longitudinal (2000 to 2013) anonymised primary care records of 286,715 patients registered at 125 randomly selected general practices within CPRD. Data were reported in financial years. Prevalence of diabetes in patients with and without SMI was identified for each year using previously validated clinical codes. We used the presence of test data for HbA1c, cholesterol and blood pressure as indicators of diabetes monitoring and test values to investigate diabetes control. The percentage of patients who had test data for each year was recorded. Test values were taken for each year; because of the non-linear relationship between diabetic control and mortality, mean values were dichotomised as being, or not being associated with increased risk of mortality. Logistic regressions were conducted to compare for each test, the percentage of people who had test data, and test values indicating risk of mortality between SMI and non-SMI patients with diabetes, controlling for age and gender.

Findings

Overall, diabetes monitoring in all patients with diabetes increased over time. From 2000 to 2013, the percentage of patients with at least one recorded cholesterol test per year increased from 28.2% to 86.3%; for HbA1c tests it increased from 12.3% to 92.0%; and for blood pressure from 66.0% to 94.5%. There were no differences between the SMI and non-SMI patients for monitoring of cholesterol, HbA1c and blood pressure. There were differences in diabetes control between the two populations. Patients with comorbid diabetes and SMI were more likely to have test values associated with mortality for cholesterol (OR=1.20, 95%CI=1.08-1.35, p=0.001), HbA1c (OR=1.19, 95%CI=1.11-1.27, p=<0.001) and systolic blood pressure (OR=1.43, 95%CI=1.35-1.52, p=<0.001) compared to people with diabetes and no SMI. For diastolic blood pressure, however, patients with comorbid diabetes and SMI were less likely to have test values associated with mortality (OR=0.94, 95%CI=0.88-0.99, p=0.045).

Consequences

Despite similar levels of diabetes monitoring, there appear to be disparities in diabetic control for adults with comorbid SMI and diabetes compared to adults with diabetes and no SMI. Given the impact of diabetes control on morbidity and mortality, further research is needed to understand and address these differences.