Validity of diabetes self-reports in the Women's Health Initiative: comparison with medication inventories and fasting glucose measurements

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Abstract
Objective: Although diabetes is conveniently assessed by self-report, few validation studies have been performed. Therefore, we studied whether self-report of prevalent and incident diabetes in Women's Health Initiative (WHI) participants was concordant with other diagnostic evidence of diabetes. Study Design and Setting: A total of 161 808 postmenopausal women aged 50—79 were enrolled at 40 clinical centers in the U.S. in 1993—1998 and followed prospectively. At baseline, prevalent medication treated diabetes was defined as a self-report of physician diagnosis and treatment with insulin or oral antidiabetic drugs. During followup, incident treated diabetes was defined as a self-report of a new physician diagnosis of diabetes treated with insulin or oral drugs. Diabetes self-reports were compared with medication inventories and fasting glucose levels at baseline and during follow-up. Results: At baseline, self-reported treated diabetes was concordant with the medication inventory in 79% of clinical trial, and 77% of observational study participants. Self-reported incident treated diabetes was concordant with the medication inventory in 78% between baseline and Year 1 in the clinical trials, in 62% between Year 1 and Year 3 in the clinical trials, and in 72% between baseline and Year 3 in the observational study. Over similar periods, 99.9% of those who did not report treated diabetes had no oral antidiabetic drugs or insulin in the medication inventory. At baseline, about 3% not reporting diabetes had fasting glucose >126 mg/dl, and 88% of these subjects subsequently reported treated diabetes during 6.9 years of follow-up. Limitations: Incident self-reported diabetes treated by lifestyle alone was not determined in WHI. Medication inventories may have been incomplete and fasting glucose may have been lowered by treatment; therefore, concordance with self-reported treatment or fasting glucose ≥ 126 may have been underestimated. Conclusion: In the WHI, self-reported prevalent and incident diabetes was consistent with medication inventories, and a high proportion of those with undiagnosed diabetes subsequently reported diabetes treatment. Self-reports of `treated diabetes' are sufficiently accurate to allow use in epidemiologic studies. Clinical Trials 2008; 5: 240—247. http://ctj.sagepub.com