*Purpose: Implementation of molecular biomarkers in kidney transplantation has expanded the amount of information available to clinicians before deciding to pursue biopsy. We evaluated how use of donor-derived cell-free DNA testing (dd-cfDNA) impacts histologic biopsy yield.

*Methods: 1663 kidney transplant (KTx) recipients enrolled in the Kidney allograft Outcomes AlloSure Registry (KOAR, NCT03326076) were followed with dd-cfDNA post-transplant; testing was obtained either as part of a surveillance strategy or for-cause; indications for biopsy and histologic diagnoses were captured. This analysis included only for-cause biopsies.

*Results: 65 biopsies (from 59 pts) driven by elevated dd-cfDNA levels were compared to 540 biopsies (392 pts) obtained for causes other than elevated dd-cfDNA. Patient age (55 vs 56 years), percent deceased donor (84.75% vs 78.83%), and biopsy timing post-transplant (123 vs 105.5 days) did not differ between groups [Table 1]. Among dd-cfDNA-guided biopsies, yield was enriched for rejection (48% vs 29%) and included fewer cases of ATI/ATN (12% vs 22%) compared to biopsies obtained for other causes (p<0.05) [Figure 1]. Among dd-cfDNA-guided biopsies with rejection (ABMR, TCMR, or Mixed), median dd-cfDNA was 1.46% (IQR: 1.15 – 2.87). Among biopsies not performed due to elevated dd-cfDNA but with paired results available (n = 267), median dd-cfDNA was 0.24%. Within this group, patients with rejection had median dd-cfDNA of 0.82% and demonstrated an increase of 133% from the preceding result.

*Conclusions: Dd-cfDNA surveillance enhances the histologic yield for actionable results in for-cause allograft biopsies. A low dd-cfDNA result can obviate the need for biopsy even in the presence of other clinical factors that are routinely used to guide the biopsy decision.

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