Renal tubular abnormalities in infants with hydronephrosis

Purpose: Abnormalities in renal tubular function have been observed in hydronephrotic urinary tract disease, resulting in metabolic acidosis, hyperkalemia and excessive free water diuresis. The frequency of these abnormalities, particularly in our infant population, was the impetus for our study. Materials and Methods: We studied 50 infants selected from 199 patients followed for hydronephrosis before any surgical intervention during a 5-year period. Mean patient age was 1.5 +/- 1.0 months at the time of diagnosis by ultrasound, voiding cystourethrography and a radionuclide renal scan. Lesions were classified as unilateral or bilateral and graded according to severity of renal pelvic dilatation or grade of vesicoureteral reflux. Results: At least 1 abnormality of tubular function was present in 29 patients (58%) of whom the predominant abnormality was renal tubular acidosis in 23 (79%, 46% of the total study group). Renal tubular acidosis was diagnosed on the basis of a serum total carbon dioxide of 19 mM./l. or less with urinary pH 5.5 or greater. The defect appeared to be distal in most cases. Other abnormalities included defects in urinary concentrating ability in 10 patients (4 with unilateral urinary tract dilatation). Distal tubular aldosterone resistance in 6 patients (3 with unilateral dilatation) was demonstrated by hyperkalemia with a low transtubular potassium gradient of 3 or less and low fractional excretion of potassium. Although common in unilateral lesions, renal tubular dysfunction became more prevalent with an increase in severity score and bilaterality. Conclusions: Renal tubular dysfunction is frequent in hydronephrotic infants with unilateral or bilateral disease. Although rarely life threatening and usually self-limiting, the metabolic consequences of these abnormalities require investigation to allow for appropriate medical management.