*Purpose: Subclinical antibody mediated rejection (sAMR) is associated with inferior graft outcomes but its diagnosis relies on the presence of biomarkers as well as histology. Donor Derived Cell-Free DNA testing (dd-cfDNA) values >1% have previously been described to predict AMR in patients with graft dysfunction. We describe rates of sAMR in clinically stable kidney recipients undergoing biopsy for de novo DSA (dnDSA) and correlate dd-cfDSA values in a subset

*Methods: Retrospective chart review of all renal allograft biopsies performed at our transplant center from January 2016 – August 2018 for the indication of dnDSA and stable graft function. Our practice initiated biopsy of all patients with stable graft function and dnDSA (screened at 1, 6, 12 mo and annually) in January 2016. Protocol dd-cfDSA screening of all recipients at months 1, 2, 3, 4, 6, and quarterly began in January 2018.

*Results: 70 biopsies were performed for the indication of dnDSA with preserved allograft function. 39 of 70 (56%) clinically stable patients showed pathological lesions consistent with sAMR. 15 of 70 patients had dd-cfDNA testing performed within 6 months of biopsy. Using the previously published cutoff of 1%, dd-cfDNA demonstrated 43% sensitivity and 100% specificity for predicting sAMR findings on biopsy of stable patients with dnDSA (table 1). A receiver operating characteristic curve identified a lower and more robust dd-cfDNA cutoff value of 0.46%, which demonstrated 86% sensitivity and 100% specificity for predicting sAMR findings on biopsy of stable patients with dnDSA (table 2).

*Conclusions: Allograft biopsy in kidney recipients with stable graft function and dnDSA detected by screening will reveal a majority with lesions consistent with sAMR. Using dd-cfDNA testing with a cutoff below the previously published value used for graft dysfunction may help to identify clinically stable recipients with dnDSA that are at high risk for sAMR lesions on biopsy.

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