Self-reported diabetes is a valid outcome in pragmatic clinical trials and observational studies

Abstract

The Centers for Disease Control estimates that approximately 24 million adults, or about 8% of the US population, are considered to have diabetes (both diagnosed and undiagnosed) [[1]Centers for Disease Control and PreventionNational diabetes fact sheet: national estimates and general information on diabetes and prediabetes in the United States, 2011. U.S. Department of Health and Human Services Centers for Disease Control and Prevention, Atlanta, GA2011Google Scholar]. The risk of developing diabetes increases with age, more so for women compared with men [2Harris M.I. Flegal K.M. Cowie C.C. Eberhardt M.S. Goldstein D.E. Little R.R. et al.Prevalence of diabetes, impaired fasting glucose, and impaired glucose tolerance in US adults. the Third National Health and Nutrition Examination Survey, 1988-1994.Diabetes Care. 1998 Apr; 21: 518-524Crossref PubMed Scopus (2432) Google Scholar, 3DECODE Study GroupAge- and sex-specific prevalences of diabetes and impaired glucose regulation in 13 European cohorts.Diabetes Care. 2003; 26: 61-69Crossref PubMed Scopus (454) Google Scholar, 4Owens M.D. Beckles G.L. Ho K.K. Gorrell P. Brady J. Kaftarian J.S. Women with diagnosed diabetes across the life stages: underuse of recommended preventive care services.J Womens Health (Larchmt). 2008; 17: 1415-1423Crossref PubMed Scopus (30) Google Scholar]. The Women’s Health Initiative (WHI) is a data source that has tremendous untapped potential for exploring the risk factors for and the health consequences of diabetes in older women. From 1993 to 1998, the WHI enrolled 68,133 postmenopausal women, aged 50–79 years at baseline in its randomized controlled clinical trials [5Anderson G.L. Manson J. Wallace R. Lund B. Hall D. Davis S. et al.Implementation of the Women’s Health Initiative study design.Ann Epidemiol. 2003; 13: S5-17Abstract Full Text Full Text PDF PubMed Scopus (550) Google Scholar, 6Hays J. Hunt J.R. Hubbell F.A. Anderson G.L. Limacher M. Allen C. et al.The Women’s Health Initiative recruitment methods and results.Ann Epidemiol. 2003; 13: S18-S77Abstract Full Text Full Text PDF PubMed Scopus (567) Google Scholar]. The cohort has been followed-up annually through 2010 and a follow-up period through 2015 was recently funded. Incident self-reported diabetes was obtained as one of the outcomes of the clinical trials, however was not independently confirmed by review of medical records. We sought to examine the agreement of self-reports of diabetes in the WHI clinical trials with medical record review, thereby obtaining estimates of both the positive and negative predictive value of self-report.All WHI trial participants from four field centers (Minneapolis, MN; Winston-Salem, NC; Birmingham, AL; Portland, OR) who self-reported diabetes at baseline (prevalent diabetes) or during follow-up (incident diabetes) were identified. A random sample of participants without self-reported diabetes (no diabetes) was also identified from the approximately 6% of the overall WHI clinical trials cohort who had serial blood samples analyzed for fasting glucose at baseline and years 1, 3, or 6. Women were surveyed regarding diagnosis and treatment. Medical records were obtained and reviewed using a protocol designed in accordance with the American Diabetes Association definition of diabetes (i.e., documented treatment with antidiabetic medications or physician diagnosis of diabetes supported by laboratory measurements of glucose) [[7]American Diabetes AssociationReport of the expert committee on the diagnosis and classification of diabetes mellitus.Diabetes Care. 1997; 20: 1183-1197Crossref PubMed Scopus (7517) Google Scholar].A total of 1,275 eligible participants were identified. Of these, 732 consented and provided survey data. Medical records were obtained for 715 (207 prevalent diabetes, 325 incident diabetes, and 183 no diabetes). Records confirmed 91.8% (95% CI=87.0–95.0) of self-reported prevalent diabetes and 82.2% (95% CI=77.5–86.1) incident diabetes. Among those who never self-reported diabetes, there was no medical record or laboratory evidence for diabetes in 94.5% (95% CI=89.9–97.2) (Table 1).Table 1Agreement between WHI self-reports of diabetes and medical record reviewWHI self-reported diabetesDiabetes status by medical record reviewAgree95% CIDisagree95% CITotalN%N%Positive predictive valueaPositive predictive value=(true positives)/(true positives+false positives).False positiveIncident diabetes26782.277.5–86.15817.913.9–22.6325Prevalent diabetes19091.887.0–95.0178.25.0–13.0207Negative predictive valuebNegative predictive value=(true negatives)/(true negatives+false negatives).False negativeNo diabetes17394.589.90–97.20105.52.80–10.10183715Abbreviations: CI, confidence interval; WHI, Women’s Health Initiative.a Positive predictive value=(true positives)/(true positives+false positives).b Negative predictive value=(true negatives)/(true negatives+false negatives). Open table in a new tab The results of this study indicate that WHI information on self-reported diabetes status is a reliable proxy for medical record review and should result in little misclassification. Indeed, the false negative (i.e., percentage of those who do not self-report diabetes who in fact would be found to have diabetes if external sources of confirmation were sought), was rather low at 5.5%. Consequently, the results of this national, longitudinal examination support the use of self-reported diabetes as a valid outcome in pragmatic clinical trials and observational studies. The Centers for Disease Control estimates that approximately 24 million adults, or about 8% of the US population, are considered to have diabetes (both diagnosed and undiagnosed) [[1]Centers for Disease Control and PreventionNational diabetes fact sheet: national estimates and general information on diabetes and prediabetes in the United States, 2011. U.S. Department of Health and Human Services Centers for Disease Control and Prevention, Atlanta, GA2011Google Scholar]. The risk of developing diabetes increases with age, more so for women compared with men [2Harris M.I. Flegal K.M. Cowie C.C. Eberhardt M.S. Goldstein D.E. Little R.R. et al.Prevalence of diabetes, impaired fasting glucose, and impaired glucose tolerance in US adults. the Third National Health and Nutrition Examination Survey, 1988-1994.Diabetes Care. 1998 Apr; 21: 518-524Crossref PubMed Scopus (2432) Google Scholar, 3DECODE Study GroupAge- and sex-specific prevalences of diabetes and impaired glucose regulation in 13 European cohorts.Diabetes Care. 2003; 26: 61-69Crossref PubMed Scopus (454) Google Scholar, 4Owens M.D. Beckles G.L. Ho K.K. Gorrell P. Brady J. Kaftarian J.S. Women with diagnosed diabetes across the life stages: underuse of recommended preventive care services.J Womens Health (Larchmt). 2008; 17: 1415-1423Crossref PubMed Scopus (30) Google Scholar]. The Women’s Health Initiative (WHI) is a data source that has tremendous untapped potential for exploring the risk factors for and the health consequences of diabetes in older women. From 1993 to 1998, the WHI enrolled 68,133 postmenopausal women, aged 50–79 years at baseline in its randomized controlled clinical trials [5Anderson G.L. Manson J. Wallace R. Lund B. Hall D. Davis S. et al.Implementation of the Women’s Health Initiative study design.Ann Epidemiol. 2003; 13: S5-17Abstract Full Text Full Text PDF PubMed Scopus (550) Google Scholar, 6Hays J. Hunt J.R. Hubbell F.A. Anderson G.L. Limacher M. Allen C. et al.The Women’s Health Initiative recruitment methods and results.Ann Epidemiol. 2003; 13: S18-S77Abstract Full Text Full Text PDF PubMed Scopus (567) Google Scholar]. The cohort has been followed-up annually through 2010 and a follow-up period through 2015 was recently funded. Incident self-reported diabetes was obtained as one of the outcomes of the clinical trials, however was not independently confirmed by review of medical records. We sought to examine the agreement of self-reports of diabetes in the WHI clinical trials with medical record review, thereby obtaining estimates of both the positive and negative predictive value of self-report. All WHI trial participants from four field centers (Minneapolis, MN; Winston-Salem, NC; Birmingham, AL; Portland, OR) who self-reported diabetes at baseline (prevalent diabetes) or during follow-up (incident diabetes) were identified. A random sample of participants without self-reported diabetes (no diabetes) was also identified from the approximately 6% of the overall WHI clinical trials cohort who had serial blood samples analyzed for fasting glucose at baseline and years 1, 3, or 6. Women were surveyed regarding diagnosis and treatment. Medical records were obtained and reviewed using a protocol designed in accordance with the American Diabetes Association definition of diabetes (i.e., documented treatment with antidiabetic medications or physician diagnosis of diabetes supported by laboratory measurements of glucose) [[7]American Diabetes AssociationReport of the expert committee on the diagnosis and classification of diabetes mellitus.Diabetes Care. 1997; 20: 1183-1197Crossref PubMed Scopus (7517) Google Scholar]. A total of 1,275 eligible participants were identified. Of these, 732 consented and provided survey data. Medical records were obtained for 715 (207 prevalent diabetes, 325 incident diabetes, and 183 no diabetes). Records confirmed 91.8% (95% CI=87.0–95.0) of self-reported prevalent diabetes and 82.2% (95% CI=77.5–86.1) incident diabetes. Among those who never self-reported diabetes, there was no medical record or laboratory evidence for diabetes in 94.5% (95% CI=89.9–97.2) (Table 1). Abbreviations: CI, confidence interval; WHI, Women’s Health Initiative. The results of this study indicate that WHI information on self-reported diabetes status is a reliable proxy for medical record review and should result in little misclassification. Indeed, the false negative (i.e., percentage of those who do not self-report diabetes who in fact would be found to have diabetes if external sources of confirmation were sought), was rather low at 5.5%. Consequently, the results of this national, longitudinal examination support the use of self-reported diabetes as a valid outcome in pragmatic clinical trials and observational studies. This study was funded by National Institute of Diabetes and Digestive and Kidney Diseases .