*Purpose: The use of procurement biopsies (Bx) to assess kidney quality is controversial. ‘Biopsy findings’ is an often cited discard reason, yet the association between Bx results and short-term outcomes is tenuous. We used UNOS’s DonorNet offer simulator, SimUNet, to conduct a controlled experiment examining the role of Bx on kidney offer acceptance decisions.

*Methods: From Nov 26-Dec 14, 2018, 68 MDs experienced in considering kidney offers (42 surgeons, 26 physicians) received 4 low creatinine (Cr<1.5 mg/dL) kidney offers with ‘questionable’ Bx findings; 4 otherwise clinically-identical offers without Bx; and 4 with ‘clean’ Bx, each for a specific potential recipient. The 4 questionable Bx offers were based on real offers that were accepted and transplanted with 2-year recipient eGFR>35. We also sent 4 non-Bx, acute kidney injury (AKI, Cr>4 mg/dL) offers and 4 otherwise clinically-identical offers but having ‘clean’ Bx. A balanced crossover design with repeated measures and a minimum washout period of a weekend was used, with statistical methods for clustered binary data.

*Results: For each low Cr donor, the acceptance rate increased markedly when Bx results changed from questionable to clean (e.g., donor A: 48.4% to 93.8% (p<0.0001), Fig 1). For each non-Bx AKI offer, the acceptance rate rose sharply when clean Bx findings were displayed (e.g., donor E: 20.6% to 49.2% (p=0.0003)). 15 (22%) MDs had responses consistent with the use of Bx to rule-out low Cr kidneys but not to rule-in AKI kidneys; 14 (21%) MDs: rule-in but not rule-out; 35 (51%) MDs: both rule-in and rule-out; 4 (6%) MDs: not influenced by Bx.

*Conclusions: In a controlled experiment, the likelihood of kidney offer acceptance nearly doubled when Bx findings were ‘clean’ compared to ‘questionable.’ The # of doctors using Bx to rule-in AKI kidneys was about equal to the # using biopsies to rule-out low Cr kidneys. Routine Bx may contribute to the unjustified discard of kidneys but may also help salvage good kidneys with questionable function. Given their profound influence on decision-making, reliability of Bx interpretation should be improved by wider use of nephropathologists, centralized interpretation, and/or automation/machine learning. Centers should be informed as to the source of Bx interpretation. Further research into the link between Bx results, outcomes, and discards is vital to help determine their proper role in transplant decision-making.

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