Estimates of kidney function in obese African Americans with chronic kidney disease

Methods for assessing glomerular filtration rate (GFR) are controversial in obese individuals. This study compared clinical estimates of GFR in African Americans (AA) with chronic kidney disease (CKD) overall and by body mass index (BMI).

The estimated GFR was determined in AA with CKD using (1) the 4-variable Modification of Diet in Renal Disease equation (MDRD4), (2) the Cockcroft-Gault equation with ideal, adjusted and total body weight (TBW, with and without normalization for body surface area), and (3) urine collection methods. Differences in mean values and CKD staging were compared for all patients and for subgroups with a BMI above and below 30.

The mean GFR by MDRD4 for individuals with a BMI of >30 was 35 ± 14 ml/min/1.73 m(2) and ranged from 32 to 53 ml/min by other methods. Estimates using TBW differed significantly from the MDRD4, a finding not observed for the lower BMI subgroup or when using adjusted weights. The obese patients were more often categorized into a less severe CKD stage, whereas the lower BMI subgroup was commonly grouped into a more severe CKD stage compared to MDRD4 staging.

Significant variations in estimated GFR between methods exist in the obese. Until other assessment methods are adequately evaluated, clinicians must be critical in applying clinical estimates of kidney function to patient care.