Methods and Limitations
The U.S. Renal Data System (USRDS) is a surveillance system for End-Stage Renal Disease (ESRD) funded by the National Institute of Diabetes and Digestive and Kidney Diseases of the National Institutes of Health. USRDS collects, analyzes, and distributes information from clinical and claims data reports to the Centers for Medicare and Medicaid Services (CMS) regarding patients being treated for ESRD. CMS reimburses most of the total cost of ESRD treatment in the United States, supplies most of the data used by USRDS, and provides expertise on data management.1
We defined ESRD-DM incidence as cases initiating treatment for ESRD (dialysis or kidney transplantation) and having diabetes listed as the primary cause of renal failure. Rates were calculated using two population estimates: 1) the resident U.S. population from the Census, and 2) the number of U.S. residents with diabetes obtained from the weighted sample of the civilian noninstitutionalized population in the National Health Interview Survey (NHIS).2 Three-year moving averages were used to improve the precision of the estimated population with diabetes, and incidence was age-adjusted on the basis of the 2000 U.S. standard population.
The USRDS dataset is a living record of ESRD care in the United States, and is continually updated with new information on the ESRD population. Delays in the reporting of data account for the changes in the reported counts of incident patients from year-to-year as late information is added to the USRDS dataset.
Ascertainment of incident cases is incomplete because the data are for persons receiving ESRD treatment as reported to CMS and do not include patients who die of ESRD before receiving treatment and those who are not reported to CMS. Because the incidence of ESRD-DM was defined in terms of initiation of ESRD treatment, changes in incidence may have been due to changes in factors other than disease incidence. These include changes in treatment and care practices, greater recognition of the etiologic role of diabetes in ESRD, better access to ESRD treatment or acceptance of treatment, or a combination of these factors.3
In 1996, the NHIS estimate of the number of U.S. residents with diabetes was unusually low. Relative to 1995, the 1996 NHIS sample size was reduced by approximately 25% in the first and second quarters and by approximately 50% in the third and fourth quarters. Beginning in 1997, the NHIS survey methodology was changed;2 instead of asking a one-sixth subsample of respondents whether during the preceding 12 months a family member had diabetes, all sampled adult respondents were asked whether a health professional had ever told them they had diabetes. The low estimate in 1996 and the survey redesign in 1997 resulted in a large increase in the estimated number of people with diagnosed diabetes between 1996 and 1997.
CMS began collecting Hispanic ethnicity data in 1995 and NHIS began collecting it in 1997. Therefore, for ESRD-DM incidence trends, race and ethnicity were considered independently. Persons who identified themselves as black or white might be Hispanic or non-Hispanic, and persons who identified themselves as Hispanic might be of any race.
NHIS underestimates the true prevalence of diabetes. Estimates from the National Health and Nutrition Examination Survey suggest that nearly 30% of adults with diabetes do not know they have it.4
- United States Renal Data System. Available at http://www.usrds.org.*
- Centers for Disease Control (CDC). 1997 National Health Interview Survey (NHIS) Public Use Data Release: NHIS Survey Description. Hyattsville, MD: US Department of Health and Human Services, 2000. Available at ftp://ftp.cdc.gov/pub/health_statistics/nchs/dataset_documentation/nhis/1997/srvydesc.pdf (PDF – 134 KB).
- Nelson RG, Knowler WC, Pettitt DJ, Bennett PH. Kidney diseases in diabetes. In: Diabetes in America. 2nd edition Harris MI, Cowie CC, Stern MP, Boyko EJ, Reiber GE, Bennett PH, editors. Washington, DC: US Department of Health and Human Services, National Institutes of Health; 1995. DHHS publication no. (NIH)95-1468; 361−366.
- Centers for Disease Control and Prevention. National Diabetes Fact Sheet: National Estimates and General Information on Diabetes and Prediabetes in the United States, 2011. Atlanta: U.S. Department of Health and Human Services; Centers for Disease Control and Prevention, 2011.
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