*Purpose: The current Organ Procurement and Transplantation Network (OPTN) policy on living kidney donors (LKD) require that all LKD candidates have measured glomerular filtration rate (mGFR). In 2017, the Kidney Disease Improving Global Outcomes (KDIGO) Living Donor Work Group recommendations state that donors’ renal function can be confirmed using Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) study equation using creatinine alone (eGFRcr), cystatin C alone (eGFRcys), or a combination of creatinine and cystatin C (eGFRcr-cys). There are multiple studies demonstrating eGFRcr overestimates renal function in obese patients. Given the national trend of increasing body mass index (BMI) in donors, there needs to be better understanding about how BMI affects on eGFR measurements in the LKD population. The goal of our study is to evaluate the impact of BMI on the relationship between eGFRcr, eGFRcys, eGFRcr-cys versus mGFR.

*Methods: Renal function was assessed in 181 living donor candidates via mGFR using 125-I iothalamate clearance and CKD-EPI formula using serum creatinine and/or cystatin C. Iothalamate clearance was reported as an average of four independent measurements. Patients were stratified into four groups based on their BMI, (≤18, 19-25, 26-29, ≥30kg/m²). One patient had BMI ≤18, 74 patients had BMI 19-25, 62 patients had BMI 26-29, and 44 patients had BMI ≥30. Pearson’s correlation was performed for eGFRcr, eGFRcys, and eGFRcr-cys versus mGFR in each BMI strata. Statistical analyses were performed using SAS.

*Results: Median age was 46±12 years and body surface area (BSA) 1.88 ±0.23m² in donors, 72% were female, and 86% were white. Median mGFR was 99.4ml/min/1.73m2 (range 66-140), eGFRcr 96 ml/min/1.73m2 (range 61-131), eGFRcys 99.4ml/min/1.73m2 (range 58-145), and eGFRcr-cys 97.9ml/min/1.73m2 (range 62-132). Table 1 below shows the correlation between different eGFR equations and mGFR for the four BMI strata. The correlation between eGFR and mGFR across all BMI strata was improved by utilizing eGFRcys. In patients with BMI ≤18 and 26-29, using eGFRcr-cys offered some improvement over eGFRcys.

*Conclusions: BMI does have an impact on GFR measurements. There is also a difference in how BMI affects creatinine-based and cystatin-based equations.

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