Introduction: Central body fat distribution, in which most fat is accumulated in the abdominal region, has been associated with increased risk of renal function impairment. Especially an excess of visceral fat is accompanied by an increased renal risk. Although body mass index (BMI) is facing increasing scrutiny due to its inability to accurately assess body composition, it remains the gold standard in screening guidelines for living kidney donation. Abdominal fat measurements using computed tomography (CT) may prove superior in assessing body composition related renal risk for living kidney donors. This study aimed to identify donors with high levels of total abdominal, visceral, subcutaneous or intramuscular adipose tissue (TAT, VAT, SAT, and IMAT, respectively) and determine the association with renal function before and (long term) after donor nephrectomy. Potential differences between CT-derived fat measurements and BMI, as a measure of body composition-related post-donation renal risk, were investigated.

Methods: Between 2002 and 2019, 970 living kidney donors from the University Medical Center Groningen were included in this study. Volumes of abdominal fat compartments were determined from an axial CT slice at vertebral level L3. Donors underwent glomerular filtration rate measurements (mGFR (125I-Iothalamate)) prior to donation and at 3 months, 5 and 10 years after donation. Uni- and multivariable linear regression analyses were performed to assess the association of tomographic fat measurements and BMI with renal function.

Results: Mean donor age was 53 ± 11 years and 50% were male. Multivariable linear regression analyses in both male and female donors showed that higher levels of TAT, VAT, SAT, and IMAT were all significantly associated with lower mGFR levels at screening for donation (male donors: TAT: Β=-0.06, p<0.001, VAT: Β=-0.04, p=0.002, SAT: Β=-0.06, p=0.004, and IMAT: Β=-0.36, p=0.01; female donors: TAT: Β=-0.07, p<0.001; VAT: Β=-0.06, p<0.001; SAT: Β=-0.07, p<0.001, and IMAT: Β=-0.32, p=0.01). In contrast, higher BMI was significantly associated with higher mGFR at screening (male donors: Β=1.35, p<0.001; female donors: Β=1.09, p<0.001). Long-term after donation, tomographic abdominal fat measurements remained inversely associated with mGFR in male donors. For female donors, this was only the case at 3 months after donation. Higher BMI remained associated with higher mGFR levels long-term after donation in both male and female donors.

Conclusion: This study shows that abdominal fat volume has a negative effect on renal function at time of screening and (in male donors) long-term after living kidney donation. In contrast, BMI was associated with higher mGFR levels during screening and long-term after donation. Comprehending the renal outcomes of living kidney donation and accurately identifying their body composition related risk factors can aid clinicians in decision-making and donor counseling during screening for donation.