*Purpose: Donor derived cell-free DNA (dd-cfDNA) has emerged as a marker of kidney allograft injury. Beginning in 2019, the dd-cfDNA monitoring has been introduced as the standard of care in the surveillance of post kidney transplant patients. in attempt to confirm its ability to better able to discriminate active rejection and quantify allograft injury.

*Methods: Eighty three patients were surveyed with dd-cfDNA at regular time points, collected at the time of surveillance biopsies at 3 and 12 months post transplant. Donor-specific antibodies (DSA), CMV and BKV were also monitored at the same time. Donor derived-cf-DNA were also performed for clinical concern to assess the need for invasive biopsies in clinically challenging patients.

*Results: A total of 64 patients showed no active rejection: dd-cfDNA levels were normal in 56 (87.5%); eight patients had elevated dd-cfDNA with no evidence of rejection (4 BK Viremia, 2 FSGS, 1 Membranous GN and 1 other). The remaining 19 patients were found to have active rejection (11 borderline, 4 TCMR 1A, 2 TCMR 2A, 2 chronic AMR). The median dd-cfDNA was 0.93% (0.49-1.7%) in all patients with active rejection. For those with AMR, the median dd-cfDNA was 3.4% and for TCMR, the median dd-cfDNA was 0.45% . Patients with rejection had a median creatinine of 1.16 mg/dl (0.87-1.79) , which was similar to those without rejection, having a median creatinine of 1.1 mg/dl (1.06-1.70) (Figure 1- see below)

*Conclusions: The use of dd-cfDNA in the care of transplant patients in a community setting can help facilitate and optimize care by better targeting those patients who need to be aggressively surveilled and treated for rejection. Therefore, using dd-cfDNA in the post transplant period can very useful and superior to creatinine alone, allowing for the detection of subclinical rejection identified by surveillance biopsies.

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