Introduction: The continued utility of routine surveillance mercaptoacetyltriglycine-3 (MAG-3) renal scan within 48 hours post-kidney transplant in all patients for detecting early acute kidney injury and prognosticating time to recovery needs to be evaluated.
Methods: In this retrospective analysis, time to creatinine nadir (TTN) represented timeliness of recovery, and recipient unfiltered glomerular filtration rate at 3-months post-transplant (uGFR_{R 3mo}) represented extent of recovery. Four MAG-3 scan parameters, time to peak activity, peak to half peak time, 30 min/peak ratio and 30 min/3 min ratio, were analyzed. A cox and linear regression model, each including clinical and MAG-3 covariates, was built to assess the utility of MAG-3 renogram metrics to improve graft outcome prognostication. 
Results: 67 patients (58% male, aged 13 (IQR 7, 16) years at transplant) were included. Clinical factors associated with TTN included younger donor age (ρ=-0.39, p<0.001), deceased donor type (p=0.002) and longer cold ischemic time (ρ =0.28, p=0.020). Clinical factors correlated with uGFR_{R 3mo} included older recipient age (ρ=0.68, p<0.001), larger recipient body surface area (BSA) (ρ=0.65, p<0.001), donor male sex (p=0.018) and deceased donor type (p=0.008). All four MAG-3 metrics correlated with TTN but not with uGFR_{R 3 mo}. The addition of MAG-3 scan indicators improved the modelling for TTN. The optimal model included recipient BSA, donor age, Cr 24h/0h, MAG-3 peak to half peak time and 30 min/peak ratio (R²=0.33, AIC=348, p<0.001), which was 8% better than the model including only clinical factors (R²=0.25, AIC=422, p<0. 001). The best-fitted uGFR_{R 3mo} model included donor and recipient BSA (adjusted R²=0.40, AIC=571, p<0.001), where adding the MAG-3 indicators of peak to half peak time and 30 min/peak ratio did not improve the modelling despite the reduced model complexity (adjusted R²=0.40, AIC=498, p<0.001). Radiologic interpretation identifying delayed graft function/acute tubular necrosis based on the MAG-3 results was strongly associated with TTN. Actionable early surgical complications including urinary leak and photopenic areas indicating regional ischemia/infarction were also revealed.
Conclusion: This is the first study to evaluate and demonstrate the utility of early post-transplant MAG-3 scans in pediatric patients. This study highlights the utility for the MAG-3 scan to identify the severity of peri-operative injury that manifests as slower functional recovery but not requiring post-operative dialysis, and for early diagnosis in the minority of cases with potentially actionable post-operative complications. Further evaluation is needed to understand the utility of the MAG-3 scan in evaluating the extent of functional recovery post-transplant in pediatric patients. This data supports continued use in post-transplant monitoring.