Depression increases both glycated haemoglobin testing frequency and risk of all-cause mortality in type 2 diabetes

BackgroundFrequent and consistent Glycated Haemoglobin (HbA1c) measurement is required for effective management of Type 2 diabetes (T2D). Co-morbid depression is an important driver of poor health and mortality in individuals with T2D. Little is known about how engagement with primary care for T2D management differs in individuals with co-morbid depression, and how this impacts all-cause mortality. MethodsAdults with T2D were identified in the Clinical Practice Research Datalink Aurum dataset. Glycaemic testing frequency was defined as the number of HbA1c measurements per year after diagnosis. Conway-Maxwell-Poisson mixed effects models were used to test the associations between glycaemic testing frequency and T2D co-morbidities, pre-existing and incident depression (after T2D diagnosis), and depression severity. Cox proportional hazard models were used to determine the association of these variables with all-cause mortality. ResultsIn total, 470,225 individuals with T2D were included. Of these, 20.1% and 6.1% had pre-existing and incident depression, respectively. Younger age, male sex, and non-White self-reported ethnicity were robustly associated with lower glycaemic testing frequency. In contrast, higher deprivation, pre-existing depression (IRR:1.06, CI: 1.05 - 1.07, p = 6.5x10-11), incident depression (IRR:1.04, CI: 1.03 - 1.05, p = 5.5x10-11) and a higher incident comorbidity score were associated with more frequent HbA1c testing. Pre-existing depression, incident depression, and depression severity were associated with increased risk of all-cause mortality after adjusting for HbA1c testing frequency (incident depression HR: 1.41, CI: 1.37 - 1.45, p = 3.7x10-97). In the entire cohort, higher HbA1c testing frequency was associated with reduced risk of all-cause mortality (HR: 0.93, 95% CI: 0.92 - 0.94, p = 3.60x10-82). ConclusionIndividuals with T2D and depression have more frequent glycaemic testing yet still face a higher risk of mortality. This suggests that increased engagement with primary care for glycaemic monitoring alone is not sufficient to offset the broader health risks associated with depression. Targeted interventions beyond increased routine diabetes monitoring may be necessary to reduce excess mortality among individuals managing both T2D and depression.