MAG-3 Renal scan is a standard test used to detect and evaluate hydronephrosis in the setting of obstruction of collecting system, determine the perfusion (blood flow) and the relative intrinsic function of each kidney. However, renal scan can help only predict the degree of differential function in each kidney with no information about the irreversibility of the lost function. Often due to some technical reasons, it is difficult to make an interpretation of the results. Moreover, the performance of it is highly operator dependent with results varying between various centres. Hence it is advisable to perform other tests including serum creatinine and urine tests to exactly characterise and estimate the kidney function. Finally, one would need to address the underlying anatomical defect in the urinary system of your child to see any significant improvement of the left kidney function.