Nonindexed versus Body Surface Area–Indexed Measured GFR Determinations as a Criterion of Living Donor Acceptance

Background When GFR is measured (measured GFR [mGFR]) using iohexol plasma clearance, results are reported both as nonindexed (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 donor. We sought to compare the difference between nonindexed and BSA-indexed mGFR in LKDs and the association with postdonation eGFR. Methods Between January 1, 2007, and January 1, 2023, 627 adult living kidney donors (LKD) at the University of Minnesota had predonation mGFR by iohexol plasma clearance and a minimum 6-month follow-up. LKD acceptance was based on a nonindexed mGFR $80 ml/min (age younger than 60 years) or $75 ml/min (age 60 years and older). Primary outcomes included eGFR at 1 year postdonation and sustained eGFR,45 ml/min per 1.73 m². Results Among 627 LKDs, 561 (90%) had both a nonindexed and BSA-indexed mGFR above the age-based threshold (concordant), while 66 (11%) had nonindexed measurements above and BSA indexed below (discordant). Compared with concordant LKDs, discordant LKDs were older (median: 54.1 versus 42.8 years, P, 0.001) and had higher body mass indices (28.0 versus 26.1, P, 0.001). At 1 year postdonation, mean eGFR was higher among concordant LKDs, although the difference in relative change from predonation eGFR measurements was similar. During a median follow-up of 2.3 years, six of 66 discordant LKDs (9%) experienced sustained eGFR,45 ml/min per 1.73 m² compared with five of 561 concordant LKDs (0.9%) (hazard ratio, 10.7; 95% confidence interval, 3.21 to 35.6). Conclusions Discordant LKDs had lower eGFR measurements postdonation and experienced a higher risk of eGFR,45 ml/min per 1.73