*Purpose: While there is randomized, multicenter data in adults that area under the time concentration curve (AUC) measurements for Mycophenolate Mofetil (MMF) can direct dosing and predict rejection events, the utility of MMF AUC measurements to predict rejection in stable pediatric kidney transplant patients is not well established.

*Methods: We performed a single-center, retrospective review from 2014-2020 of Pediatric kidney transplant recipients at the University of California, San Francisco who had MMF AUC testing at 3-4-months post- transplant. We included patients aged 1-21 years who were on MMF 3-months post-transplant and completed MMF AUC measurements. We excluded patients who were on enteric coated Myfortic sodium. MMF levels were obtained at the 0-, 1-, 2- and 4-hour mark. AUC was calculated using the following equation: 8.22 + 3.16*C0 + 0.99*C1 + 1.33*C2 + 4.18*C4 The standard dose of MMF at our center is 600-650 mg/m2/day at 3 months, and MMF dose is adjusted if needed, depending on hematological and gastrointestinal side effects as well as the presence of viral infections. Surveillance biopsies are performed at 6 months and as needed for-cause. We defined rejection as borderline change or greater on kidney biopsy based on 2017 Banff criteria. We analyzed the association between AUC and biopsy-proven rejection or donor specific antibodies (DSA) using logistic regression.

*Results: Fifty-one patients aged 2-21 met our criteria for inclusion (47% female). All patients were on tacrolimus immunosuppression and 40 (78%) were taking prednisone. Twenty-one patients had biopsy confirmed rejection (41%) and 5 had positive DSA (10%). We did not find a significant association between AUC and biopsy-proven rejection (p = 0.21, 95% CI 0.93 – 1.01) or DSA formation (p = 0.12, 95% CI 0.98 – 1.15). Data analysis on STATA program proved that AUC was not statistically significantly associated with rejection (OR 0.97, p 0.21, 95% CI 0.93 – 1.01) (logistic regression, rejection defined as borderline change or greater). There was no significant association between MMF AUC and same day tacrolimus trough levels, gender or BMI.

*Conclusions: We did not identify an association between four-point MMF AUC levels at 3 months post-transplant and biopsy-proven rejection or formation of DSA in pediatric kidney transplant recipients receiving tacrolimus-based immunosuppression. MMF AUC testing is time consuming and costly. It may lack utility in this population

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