Background. Body mass index (BMI) is a convenient measure used to assess obesity and is used to select candidates for kidney donation. Glomerulomegaly is an early indicator of obesity-related kidney disease. Whether obesity assessment by BMI best reflects underlying glomerulomegaly and is predictive of adverse changes in renal function postdonation is unclear. Methods. We performed a retrospective study on a cohort of 1065 living donors at the Mayo Clinic in Rochester; obesity measures by BMI and by computed tomography were compared between 20 donors with largest to 20 donors with the smallest glomerular volumes (on implantation biopsy). In addition, the change in kidney function postdonation (mean 7 months) was compared across BMI groups (<25, 25-29, 30-34, ≥35 kg/m2) in about 500 donors. Results. We observed that larger glomerular volume was more strongly associated with BMI per standard deviation (SD) (odds ratio [OR] =5.0, P = 0.002) than waist circumference/height2 per SD (OR = 3.9, P = 0.02), visceral fat/height2 per SD (OR = 2.4, P = 0.02), subcutaneous fat/height2 per SD (OR = 2.0, P = 0.06), renal hilar fat/ height2 per SD (OR = 1.6, P = 0.19), or peri/pararenal fat/height2 per SD (OR = 1.5, P = 0.23). Postdonation changes in glomerular filtration rate, blood pressure, and albuminuria were similar across BMI categories. Conclusions. The BMI outperforms various computed tomography measures of abdominal fat in detecting obesity-related glomerulomegaly. Despite this strong association with glomerulomegaly, short-term renal function outcomes are similar across BMI categories. Long-term follow-up is required to definitively define the impact of obesity on kidney function after donation.
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