Non-Indexed vs. Body Surface Area Indexed Measured Glomerular Filtration Rate Determinations as a Criterion of Living Donor Acceptance.

Introduction: When GFR is measured (mGFR) using iohexol plasma clearance, results are reported both as a "non-indexed" (mL/min) and "body-surface area (BSA) indexed" to 1.73 m2. When these two values differ, there is no consensus as to which is preferable to use to determine suitability for living kidney donation (LKD). We sought to compare the difference between non-indexed and BSA indexed mGFR in LKDs and the association with postdonation estimated GFR (eGFR).

Methods: Between 1/1/2007-1/1/2023, 627 adult LKDs at the University of Minnesota had predonation mGFR by iohexol plasma clearance and a minimum six-month follow-up. LKD acceptance was based on a non-indexed mGFR ≥80 ml/min (age <60) or ≥75 ml/min (age ≥60). Primary outcomes included eGFR at one-year postdonation and sustained eGFR <45 mL/min/1.73m2.

Results: Among 627 LKDs, 561 (90%) had both a non-indexed and BSA indexed mGFR above the age-based threshold (concordant), while 66 (11%) had non-indexed measurements above and BSA indexed below (discordant). Compared to concordant LKDs, discordant LKDs were older (median: 54.1 years vs. 42.8 years, p <0.001) and had higher body mass indices (28.0 vs. 26.1, p <0.001). At one-year postdonation, mean eGFR was higher among concordant LKDs, although the difference in relative change from pre-donation eGFR measurements was similar. During a median follow up of 2.3 years, six out of 66 (9%) discordant LKDs experienced sustained eGFR <45 mL/min/1.73m2 compared to five out of 561 (0.9%) concordant LKDs (hazard ratio: 10.7, 95% confidence intervals: 3.21 to 35.6).

Conclusion: Discordant LKDs had lower eGFR measurements postdonation and experienced a higher risk for eGFR <45 mL/min/1.73m2.