*Purpose: Donor derived cell free DNA (dd-cfDNA) is a biomarker useful in predicting acute rejection in kidney allografts. Baseline dd-cfDNA levels are <1% in 96% of kidney transplant recipients (KTRs) and a value≥ 1% suggests allograft injury usually from acute rejection. dd-cfDNA levels <1% are generally considered as normal. Current study evaluated the impact of donor type, cold ischemia time (CIT) and type of induction on baseline dd-cfDNA values.

*Methods: Patients who underwent kidney transplantation at our center between September 2017and June 2020 and had dd-cfDNA (AlloSure, CareDx, Brisbane, CA) levels at or around 8 weeks post-transplantation were identified. KTRs with normal 8-week baseline dd-cfDNA levels <1.0% were included in the analysis. Impact of donor type (living, donation after brain death [DBD], donation after circulatory death [DCD]), CIT and induction received (Thymoglobulin or basiliximab) on 8-week dd-cfDNA was then analyzed.

*Results: There were 111 patients included in the analysis including 62 males. Among the study group, 39 underwent living, 55 had DBD and 17 received DCD donor kidneys. CIT was <12 hours in 63 patients and ≥12 hours in 46 patients with data missing in 2. Thymoglobulin was the induction agent in 101 patients while basiliximab was used in 10. There were no significant differences in baseline dd-cfDNA values for living vs. DBD vs. DCD donor type (median [IQR]: 0.26%[0.19-0.43] vs. 0.24% [0.18-0.36] vs. 0.21% [0.17-0.42], p=0.59, fig.1a), CIT <12h vs. ≥ 12h (0.23% [0.17-0.47] vs. 0.26%[0.19-0.40], p=0.68, fig.1b) or Thymoglobulin vs. basiliximab induction (0.25% [0.18-0.41] vs. 0.23% [0.19-0.40], p=0.66, fig.1c).

*Conclusions: Our analysis showed similar baseline dd-cfDNA levels between living and deceased donor KTRs even though DBD and DCD kidneys are prone to higher levels of ongoing injury from factors such as ischemia-reperfusion and higher degrees of immunological mismatch. Despite the potential contribution of prolonged CIT towards allograft injury through ischemia-reperfusion, this did not translate into appreciable impact on dd-cfDNA levels. More robust suppression of early immunological injury from depleting induction with Thymoglobulin did not impact baseline dd-cfDNA levels. The current analysis suggests that peri-transplant variables may have only minimal impact on baseline dd-cfDNA levels. Relatively small sample size is a study limitation.

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