ASSESSMENT OF PEDIATRIC HYDRONEPHROSIS USING OUTPUT EFFICIENCY

Diagnosing obstruction in pediatric patients with hydronephrosis, and renal impairment is often difficult. Renal output efficiency (OE) is a parameter that may improve diagnostic accuracy by allowing normalizat ion of washout according to renal function. The aims of this study wer e to define a normal range for OE in infants and children and to evalu ate its diagnostic accuracy in cases with hydronephrosis. Methods: Sev enty-four children (91 hydronephrotic kidneys; median age, 4 mo; 22 gi rls and 52 boys) underwent Tc-99m-labeled mercaptoacetyl-triglycine sc intigraphy using intravenous volume expansion (15 ml/kg normal saline) , furosemide diuresis and urethral catheterization, if vesicoureteric reflux was present. Images were interpreted by consensus of two or mor e experienced observers using visual assessment of the images, differe ntial function and clearance half-time after furosemide (T1/2) as well as OE. The final diagnosis was based on surgical findings (n = 23 kid neys) or follow-up for >12 mo (n = 68). Results: Final diagnosis in 22 of the 91 hydronephrotic kidneys was obstruction at the pelviureteric (n = 21) or vesicoureteric (n = 1) junction and no obstruction in the remaining 69. The overall diagnostic accuracy of OE was 89%. Using ex haustive search multivariate logistic regression analysis, only reduce d OE (p < 0.001) and decreased renal uptake by visual assessment (p = 0.058) were independently predictive of obstruction (R-2 = 0.726). In dilated but unobstructed kidneys, mean OE was 93% +/- 7.1%. In the nor mal kidneys, mean OE was 96% +/- 3.1%. Conclusion: OE improves the dia gnostic accuracy of diuretic renography in children and neonates with hydronephrosis and suspected obstruction. Output efficiency should exc eed 89% in normal kidneys and 79% in unobstructed, hydronephrotic kidn eys.