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 the se abnormalities, particularly in our infant population, was the impet us for our study. Materials and Methods: We studied 50 infants selecte d from 199 patients followed for hydronephrosis before any surgical in tervention during a 5-year period. Mean patient age was 1.5 +/- 1.0 mo nths at the time of diagnosis by ultrasound, voiding cystourethrograph y and a radionuclide renal scan. Lesions were classified as unilateral or bilateral and graded according to severity of renal pelvic dilatat ion or grade of vesicoureteral reflux. Results: At least 1 abnormality of tubular function was present in 29 patients (58%) of whom the pred ominant 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 a bnormalities included defects in urinary concentrating ability in 10 p atients (4 with unilateral urinary tract dilatation). Distal tubular a ldosterone resistance in 6 patients (3 with unilateral dilatation) was demonstrated by hyperkalemia with a low transtubular potassium gradie nt of 3 or less and low fractional excretion of potassium. Although co mmon in unilateral lesions, renal tubular dysfunction became more prev alent 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 abnormalit ies require investigation to allow for appropriate medical management.