*Purpose: The longitudinal dd-cfDNA patterns in en-bloc kidney transplant recipients have not been studied. It is unknown how the initial smaller mass of the two pediatric organs impacts dd-cfDNA early post-transplant or if the dd-cfDNA rises over time as the organs enlarge. We analyzed dd‐cfDNA scores over the first 12 months in recipients of pediatric en-bloc kidneys enrolled in the Kidney allograft Outcomes AlloSure Registry (KOAR, NCT03326076).

*Methods: 16 recipients of pediatric en-bloc kidneys with donors aged ≤7 years old were identified and compared with 931 single, non en-bloc deceased donor recipients. Patients with rejection were excluded.

*Results: Of the 16 en-bloc recipients, 56.2% were male with median donor age of 1.4 years and median cold ischemia time (CIT) of 20 hours. None of the en-bloc transplants had delayed graft function. Aside from KDPI, donor age, and recipient age, no other differences were observed between groups [Table 1]. Higher median dd‐cfDNA values were seen in the en-bloc cohort compared to not en-bloc at month 1 (M1, 1.4% vs 0.4%) and month 2 (0.58% vs 0.23%) after transplant (p<0.001) [Figure 1a]. Median dd-cfDNA values were comparable for month 3 (0.21% vs 0.16%, p = 0.07) and all subsequent time points [Figure 1a, 1b]. Among 8 patients with M1 dd-cfDNA results, there was no significant association between M1 dd-cfDNA and either CIT (r=0.33, p=0.419) or KDPI (r=0.23, p=0.589) [Figure 2].

*Conclusions: Our results demonstrate higher early post-transplant dd-cfDNA values among en-bloc kidney compared to single kidney recipients however, no difference or upward trend is observed beyond month 2 and out to 12 months.

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