Maximum urinary concentration ability in patients with idiopathic hydronephrosis.

The maximum urinary concentration ability and renal parenchymal function of each kidney were investigated in 34 patients with unilateral hydronephrosis. The ability to concentrate urine was not reduced in 10 hydronephrotic and 24 contralateral kidneys. The concentration ability was moderately reduced in 14 hydronephrotic and 10 non-hydronephrotic kidneys and severely impaired in 10 hydronephrotic kidneys. A reduced concentration ability was found almost entirely in hydronephrosis complicated with upper urinary tract infection or renal calculi. Hydronephrotic kidneys without these complications showed a normal concentration ability in 10 of 11 cases. Parenchymal function was reduced in only 10 hydronephrotic kidneys, 7 of which had had upper urinary tract infections and 3 of which had renal stones. It is our opinion that uncomplicated cases of unilateral hydronephrosis should not be operated upon unless necessitated by signs and symptoms. Measurement of the maximum urinary concentration ability might be helpful in setting the correct indication for surgery in borderline cases.