*Purpose: Donor-derived cell free DNA (dd-cfDNA) is increasingly used to monitor for allograft rejection. The relationship of dd-cfDNA to donor and recipient variables in not well described. We studied impact of donor and recipient variables on dd-cfDNA.

*Methods: Serial dd-cfDNA samples were obtained in the context of routine clinical care at months 1,2,3,4, 6, 9 and 12 months post-transplant in the 1^st year post-transplant and every three months thereafter. Patients with biopsy proven acute rejection (BPAR) were excluded from the analysis. We compared the previous reported coefficient of variation (CV) 6.8% with our center’s intra-individual (CVI) and inter-individual (or group, CVG), coefficients of variation, and the reference change value (RCV).

*Results: In 111 patients: mean age: 51.7 years, 72% ;males, 89% ;Caucasian, and 48.7% ; deceased donor kidney transplants (Table 1). The means for cold ischemia time (CIT), Kidney Donor Profile (KDPI), Calculated Panel Reactive Antibody (cPRA) were 8.7 hours, 44.4%, and 13.6% respectively. Donor or recipient BMI, age, primary disease had no correlation with dd-cfDNA. Median dd-cfDNA at one month were not significantly different amongst donation after cardiac death, donation after brain death, living related and living unrelated donors (0.32, 0.32,0.31,0.27 ). Median dd-cf DNA at one month for patients with re-transplants (n=13) were significantly higher than first transplant (n=105) (p=0.0003), but not for en-bloc kidneys (n=3). (Figure 1). dd-cfDNA was positively correlated with cPRA (p=0.0008), but not with CIT and KDPI (Figure 2,3,4). Thymoglobulin induction was associated with higher median dd-cfDNA at one month compared to basiliximab induction (p=0.015). Of the 551 blood samples, dd-cfDNA values were less than 0.5% for 494 (89.6%) blood draws, 41(7.5%) were >0.5% – 1%, and 16 (2.9%) were >1% . In the 57 patients with detectable measurements for dd-cfDNA, the CVI was 30.04%, CVG was 66.5%, and RCV was 141%.

*Conclusions: Contrary to expectations, our study shows that CIT, KDPI do not have a bearing on dd-cfDNA at one month. Patients with retransplants have a significantly higher dd-cfDNA when compared to first transplants. Our reference range for dd-cfDNA in stable kidney transplants is similar to previous studies. Our RCV points out that in stable kidney transplant population, a serial increase of less than 141% in dd-cfDNA may be attributable to biological variation, whereas greater changes may be of significance. Donor and recipient characteristics and cPRA may inform cut off values prospectively.

« Back to 2020 American Transplant Congress