The findings in this report are subject to at least four limitations. First, albuminuria was used to determine kidney damage for categorizing persons as having stage 1 and stage 2 CKD, but albuminuria is not the only marker for kidney damage. Urine sediment and abnormal imaging tests also are used to determine kidney damage; however, these tests were not available in NHANES. As a result, kidney damage and reported prevalence of stage 1 and stage 2 CKD might be underestimated.5 Second, estimates for stages 1 and 2 reflect CKD indicators, rather than actual disease, because two urine samples were not available in NHANES 1999-2004 to assess persistent albuminuria and confirm the presence of kidney damage. Previous analyses of NHANES III data demonstrated that using two urine tests to confirm kidney damage produced a lesser prevalence of stage 1 and stage 2 CKD compared with using one urine test, resulting in more conservative estimates for CKD overall (11.0% versus 14.5%). Thus, CKD in this report might be overestimated.4 Third, the data are cross-sectional, not longitudinal, preventing assessment of whether risk factors caused or resulted from CKD. Finally, the number of persons with stages 3, 4, and 5 CKD is small, limiting the power of the analysis and precluding separate estimates for persons with stage 4 and stage 5 and comparison of estimates by demographic characteristic and risk factor.