*Purpose: Donor-to-recipient body weight ratios have been shown to influence kidney transplant (KT) outcomes. For small pediatric donors, this mismatch is far more pronounced and post-KT estimated glomerular filtration rate (eGFR) remains challenging to predict. To investigate this in more detail, we examined early and late post-transplant patterns specific to kidney allograft size, proteinuria and eGFR.

*Methods: Between 2007 and 2019, 45 adult recipients at Mayo Clinic Arizona were identified as receiving pediatric en bloc kidneys from donors weighing <20 kg. Results were analyzed using chi-square analysis and unequal variance t-tests. Results are shown as mean ± standard deviation.

*Results: The observed donor-to-recipient weight ratio was 0.19±0.06 (Donor weight: 12.3±3.3 kg; Recipient weight: 68.0±13.1 kg). Kidney growth was most pronounced in the first 6 months post-KT with the majority of growth occurring in the first month (p=0.0003, 48.2%) (Figure 1A-B). Relative stabilization of allograft size was noted by 1 year (Figure 1A-B). Mild proteinuria was observed in the first week post-KT (p<0.001) with the majority of patients showing resolution by 1 month post-KT (Figure 2A). Despite relative stabilization of allograft size by one year, eGFR continued to improve beyond 1 year (Figure 2B). Early (<6 months post-KT) rejection (n=4, 8.9%), cytomegalovirus (n=2, 4.4%) and BK viral (n=2, 4.4%) infections were uncommon and did not appear to impact allograft growth (p=0.9311) or eGFR (p=0.8450).

*Conclusions: Low donor-to-recipient weight ratios are observed when utilizing small (<20 kg) pediatric donors. In our cohort, significant allograft growth occurred in the first 6 months. Proteinuria was noted to resolve early and stabilize while eGFR continued to increase beyond the first post-transplant year. Robust early kidney allograft hypertrophy, specific to pediatric donors, appears to be protective against hyperfiltration injury. With mindful donor-recipient pairing, good renal function can be achieved using kidneys from smaller pediatric donors.

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