A comparison of the study populations in the Diabetes Control and Complications Trial and the Wisconsin Epidemiologic Study of Diabetic Retinopathy.

BACKGROUND: We compared the Diabetes Control and Complications Trial (DCCT) cohort with patients who had insulin-dependent diabetes mellitus (IDDM) in the Wisconsin Epidemiologic Study of Diabetic Retinopathy (WESDR) to determine whether the DCCT cohort was similar to the patients with IDDM in the general population and whether the DCCT results are generalizable to a nonresearch population.
METHODS: Demographic and clinical characteristics were compared between the DCCT study cohort and the WESDR cohort of patients with IDDM with age at onset of diabetes at younger than 30 years and followed up from 1980 to 1986. The DCCT eligibility criteria were applied to the WESDR cohort, and patients were identified who fulfilled the major criteria of the DCCT primary prevention and secondary intervention cohorts. Conventionally treated subjects in the DCCT primary prevention and secondary intervention cohorts were compared with their respective WESDR groups with regard to clinical characteristics, progression of retinopathy, and development of gross proteinuria.
RESULTS: Comparison of the DCCT primary prevention and secondary intervention cohorts at baseline with the respective WESDR groups revealed an older age and an older age at diagnosis, a lower hemoglobin A1c (HbA1c) level, and more frequent injections and monitoring in the DCCT cohorts, but there were few other substantive differences. The progression of retinopathy and the association with baseline HbA1c level were similar for the conventionally treated DCCT and WESDR cohorts, except for a lower rate of progression in the DCCT secondary intervention cohort compared with that of the WESDR cohort, perhaps because of the lower HbA1c level.
CONCLUSIONS: At baseline, patients in the DCCT cohort were generally similar to patients with IDDM in the population-based WESDR cohort, except for differences in the levels of HbA1c that diminished over time as the HbA1c levels in the WESDR cohort decreased. The demographic similarities between the DCCT and WESDR cohorts, the similar rates of progression of retinopathy in conventionally treated patients, and the similar associations between the HbA1c levels and progression of retinopathy in the DCCT and WESDR cohorts support the validity of generalizing the DCCT results to patients with IDDM in the general population.