*Purpose: Patient monitoring after kidney transplantation (KT) for early detection of allograft rejection remains key in preventing allograft loss. Donor-derived cell-free DNA (dd-cfDNA), a noninvasive surrogate for kidney biopsy is now widely used in several kidney transplant in USA in view of the reported ease of early diagnosis of acute rejection as well as avoidance of potential complications associated with kidney biopsy. More importantly, many transplant practitioners now use dd-cfDNA as a noninvasive monitor of immunological status of kidney allografts. Since January 2019, Indiana University transplant program has adopted the use of dd-cfDNA as part of diagnostic tool to evaluate kidney rejection and hereby report our experience.

*Methods: Study was a retrospective chart review of patients who received a kidney biopsy and dd-cfDNA as part of diagnostic work up for suspect acute rejection. Adult patients (>18 y/o) who underwent dd-cfDNA and Allogaft biopsy within a time a frame of 2 weeks or less between tests were included. Acute rejection was determined either by pathology has confirmed in report of kidney biopsy or by report of >1 % dd-cfDNA screen. Results were analyzed to correlate the findings on the kidney biopsy with the reports on dd-cfDNA screen.

*Results: 29 Patients with suspected rejection who underwent both donor-derived cell-free DNA (dd-cfDNA) met the inclusion criteria. 23 out of 29 patients underwent dd-cfDNA and Allograft biopsy within a time frame of 1 week. Results of our findings are presented in Table 1.

Overall, findings on kidney biopsy and dd-cfDNA report correlated in only 7 out of 29 patients (24%) included in the study. The limitation to our study includes the small sample size and the use of single point dd-cfDNA in acute rejection diagnosis.

*Conclusions: Our findings suggest negative dd-cfDNA alone should not be considered to have “rule out” rejection when pre-test probability for rejection is high especially in cases where the pretest probability for rejection is very high. Likewise, serial screen of dd-cfDNA at specific intervals may be a of a better tool either for acute rejection diagnosis or monitoring tool compared to single point screens.

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