Evaluating the effectiveness of the NHS DPP programme at reducing conversion of NDH to T2DM, using the Clinical Practice Research Datalink (CPRD)

Problem

The NHS Diabetes Prevention Programme (NDPP) is a behaviour-change programme in patients who are at risk of developing Type 2 Diabetes Mellitus (T2DM). People who have raised blood glucose levels but not in the diabetic range are identified as at risk of developing T2DM and this condition is known as Non-Diabetic Hyperglycaemia (NDH). The aim of the study was to explore the effectiveness of the NHS DPP at reducing conversion of NDH to T2DM, using the Clinical Practice Research Datalink (CPRD).

Approach

CPRD is one of the largest active primary care databases of electronic health records (EHR) in UK. We used data from the CPRD AURUM which contains data from the EMIS software system. To study the effectiveness of the programme we used data from the post-intervention period and compared NDH to T2DM conversion rate between patients referred to the scheme versus matched patients not referred, within the same practice. Patients were matched based on age (within 3 years), sex and within 365 days of NDH diagnosis. The primary outcome is conversion to T2DM within a year. Cox proportional-hazards models evaluated predictors of conversion. The final matching cohort included a total of 76,705 participants with 18,413 cases and 58,292 controls

Findings

The mean age of the cohort was 64.6(SD=12.6) years, 52% were female. The mean BMI of the cases and controls were similar (Cases: 30.8[SD=6.5]; Controls: 30.0[SD=6.3]). However, those referred were more likely to be obese. Ex or current smokers were more likely to be referred to the programme, with cases having 46% of current smokers and 35% of ex-smokers. A total of 3036 participants developed T2DM in the study period. The differences in conversion rates between the two groups will also be presented.Females were less likely to convert to T2DM with a HR of 0.9(95% CI: 0.85 to 1.00) compared to men. Individuals aged 85 years and over were less likely to develop T2DM compared to those aged 18-34, with a HR of 0.58(95% CI: 0.3 to 0.93). People with high BMI had a much higher risk of conversion to T2DM, with those classed overweight (BMI 25-30) having a HR of 1.45 (95% CI: 1.21 to 1.74), and those classed obese (BMI>=30) having a HR of 2.1 (95% CI: 1.8, 2.5), compared to individuals with a normal BMI (18.5 to 25). Having depression at baseline slightly increased the risk of conversion (HR=1.14, 95% CI 1.04, 1.24). Those who had a prescription for metformin were at a higher risk of developing T2DM with a HR of 3.3(95 % CI 2.7 to 4.2).

Consequences

Our final findings on the effectiveness of the programme will be confirmed once we also conduct further analysis which will be across practice matching to control for potential unmeasured confounding in referrals, by matching referring practices to non-referring practices over a set period