*Purpose: Biopsy findings have been shown to have a profound impact on kidney utilization decisions. Most studies of the association between procurement biopsy findings and kidney recipient outcomes have been limited in scale and focused on short-term survival. With a goal of aiding transplant decision-making, the BARETO (Biopsy, Anatomy, and Resistance Effects on Transplant Outcomes) national registry study unlocks previously trapped biopsy and anatomy data on DonorNet attachments to assess relationships between these findings and long-term renal graft outcomes.

*Methods: Data were manually entered for a preliminary cohort of 4,125 ECD donor solitary kidney transplants from 2008-2011. Interstitial fibrosis (I/F) was characterized as absent/minimal (0-5%) or mild+ (≥6%). Analyses include Kaplan-Meier all-cause graft survival and 3 types of Cox models (propensity weighted, multivariable regression, and doubly robust regression (DRR)) to adjust for 18 possible confounders.

*Results: Survival curves suggest a reduction in long term graft survival for kidneys having mild or worse I/F (p=0.022, Fig 1).

However, after risk adjustment (Fig 2) this effect was negated (HR 1.00, 95% CI: 0.90, 1.11 in DRR), suggesting these observed differences may be entirely attributable to correlations with other factors, namely glomerulosclerosis and ischemia time.

*Conclusions: Robust causal inference methods suggest that the independent association between I/F and long term graft survival is very small or non-existent, challenging this parameter’s relevance in kidney utilization decisions.

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