Correlation of Fractional Excretion of Sodium With Renal Scintigraphy and Renal Ultrasonography in Children With Unilateral Ureteropelvic Junction Obstruction Undergoing Pyeloplasty: A Prospective Observational Study.

Introduction Ureteropelvic junction obstruction (UPJO) remains a common pediatric urological condition that often requires surgical intervention, and the search for reliable markers to assess postoperative resolution is ongoing. Partial ureteral obstruction is associated with impaired sodium reabsorption; consequently, animal studies have consistently demonstrated natriuria in models of partial ureteral obstruction. Fractional excretion of sodium (FENa) reflects tubular function by measuring urinary sodium excretion and has been used to differentiate the types of acute kidney injury (AKI). To date, no published studies have evaluated preoperative and postoperative FENa in patients with UPJO to demonstrate postoperative improvement or to determine its correlation with established modalities for assessing renal function, such as renal scintigraphy. Aims This study aimed to evaluate the correlation between FENa and renal scintigraphy, specifically diethylene triamine pentaacetic acid (DTPA) renography, as well as renal ultrasonography (USG), in children with unilateral UPJO before and after pyeloplasty. Methodology A time-bound prospective observational study was conducted in the Department of Pediatric Surgery from October 2021 to April 2023. In children who met the diagnostic criteria for UPJO and required surgical intervention, a urine sample was collected intraoperatively to determine the FENa. The FENa values were then correlated with the findings of renal scintigraphy and renal USG. Results A total of 35 patients with a mean age of 7.03 ± 5.03 years were included in the study. FENa on the affected side showed a significant inverse correlation with differential renal function (DRF) (r = -0.650, p < 0.001) and renal cortical thickness on USG (r = -0.413, p = 0.009). In contrast, FENa demonstrated a significant positive correlation with the anteroposterior pelvic diameter (APPD) measured on USG (r = 0.506, p = 0.001). Discussion Our findings indicate that improvement in DRF was associated with a reduction in the FENa, suggesting improved tubular sodium handling following pyeloplasty. Greater pelvic dilatation was associated with higher FENa values, both of which decreased after pyeloplasty. Similarly, an increase in renal cortical thickness was associated with a reduction in FENa following surgery. These findings suggest that the FENa may serve as a useful surrogate marker for assessing renal function in patients with unilateral UPJO and for evaluating postoperative improvement in renal function following pyeloplasty.