Abstract
Background: The National Kidney Foundation’s Kidney Disease Outcomes Quality Initiative recommends the use of the Modification in Diet and Renal Disease (MDRD) equation to estimate glomerular filtration rate (eGFR) from serum creatinine, age, sex, and race. However, in many managed care organizations (MCOs) race is not routinely collected. The current analysis compares the use of areabased imputed race to actual race in using the MDRD equation to calculate eGFRs and to identify chronic kidney disease (CKD) in MCOs.
Methods: The study population consisted of 9,196 Kaiser Permanente Georgia members with two eGFR measures <90 ml/min/1.73m2 measured 60–365 days apart in 2007 and who had non-missing race. Residential addresses were geo-coded to 2000 U.S. Census block data. The factor of 1.210 for African American (AA) race in the MDRD formula was adjusted according to the proportion of AAs (pAA) in the Census block using the formula: 1+(0.210*pAA). We compared mean eGFR using actual race and area-based race by decile of percent AAs and by CKD stage. A weighted kappa statistic was calculated to measure the correlation between the two measures of CKD and Bland-Altman plots were constructed to measure agreement.
Results: By decile of percent AAs in the Census blocks, the differences in mean eGFR estimated using actual race and area-based race were small — ranging from 0 to 1.2 ml/min/1.73m2. A trend was observed with greater differences among those living in neighborhoods 20–80% AAs and smaller differences in neighborhoods with <20% or >80% AAs. By CKD stage, the differences in mean eGFR using actual and area-based race were also small — ranging from 0.1 to 0.4 ml/min/1.73m2. The weighted kappa statistic for the correlation between CKD stage estimated by actual versus area-based race was 0.88. Bland-Altman analysis indicated that the 95% limits of agreement between the two methods ranged from 14.2 to 12.5; and, plots demonstrated good agreement.
Conclusions: Imputing race in the MDRD formula using an area-based measure of proportion AA to calculate eGFR results in values that are comparable to eGFR computed from actual race. These results suggest that area-based race from the U.S. Census may be used to overcome limitations of missing actual race for identifying adults with CKD in MCOs.
