Severe obesity and the impact of medical weight loss on estimated glomerular filtration rate.

With severe obesity, high fat-free mass and BSA result in low estimates of eGFR indexed to 1.73m2 BSA, especially when creatinine-based estimating equations are used. GFR indexed to actual BSA is approximately 50% higher. When eGFR is indexed to actual BSA, many subjects display evidence of renal hyperfiltration which improves with weight loss. In subjects with severe obesity undergoing medical weight loss, estimating equations that use cystatin C and are indexed to actual BSA may provide a more accurate assessment of renal function.