Background: Donor– derived cell free DNA (dd–cfDNA) detected in the blood of transplant recipients has been proposed as a noninvasive marker of various types of graft injury. dd–cfDNA is a constant and dynamic marker of DNA released and cleared continuously from the allograft into recipients circulation. Elevation in dd– cfDNA may precede the changes in the relatively insensitive serum creatinine.
Objective: In this retrospective study we compared the level of dd–cfDNA and the associated change in estimated glomerular filtration rate (eGFR), at 30 days following the dd–cfDNA test.
Design/Methods: We longitudinally collected plasma samples from our pediatric kidney transplant population from 2013 onwards. dd–cfDNA was quantified in the banked plasma samples by targeted, clinical grade next– generation sequencing for single nucleotide polymorphisms (AlloSure, CareDx), Samples were drawn between 30 days and 12 months post-transplant. We extracted from the medical records the standard of care serum creatinine values, measured at time of dd–cfDNA test and again 30 days later. eGFR was estimated by CKiDScr equation, using subject height (cm) and serum creatinine (mg/dL). dd–cfDNA was categorized as high if ≥0.5% versus low if <0.5%. Percent changes in estimated GFR were evaluated using Kolmogorov ––Smirnov two sample tests, to compare the cumulative distributions.
Results: 53 patients were included in this cohort. 81 samples had elevated dd–cfDNA and 159 samples had low levels. Elevated levels of dd–cfDNA predicted greater variability in eGFR change at 30 days from the dd– cfDNA test. The low dd–cfDNA group showed a low spread of change in eGFR (mean = -1.1 %, SD = 8.5%, median = 0%, IQR −7.5% to 1.1%; Figure). In contrast, the high dd–cfDNA group showed a significantly greater spread of change in eGFR (Kolmogorov–Smirnov two sample test P = 0.0004) (mean = -1.2%, SD = 27.26%, median = 0%, IQR −19.9% to 15.77 %; Table), even with nearly identical measures of central tendency.

Conclusion(s): In terms of utility, dd–cfDNA surveillance can complement serum creatinine measurements in pediatric kidney transplantation follow up. Elevated dd–cfDNA may be more sensitive to identify allograft injury, though agnostic to type and etiology of graft injury. At 30 days later, eGFR declines could represent a developing acute rejection or intragraft infection, whereas eGFR improvements could represent a prior subclinical ischemic injury event that was recovering.