Hydronephrosis in childhood--reliability of ultrasound screening.

The reliability of gray scale sonography for the screening of hydronephrosis is assessed in a retrospective clinical study of pediatric patients. The sensitivity was 89% and the specificity 95%. Discrepancies between the ultrasound and urographic diagnosis of mild hydronephrosis--which was usually not clinically significant--accounted for all of the errors. False positive studies can be reduced by scanning the kidneys with the bladder empty. False negative examinations may be due to the contrast induced diuresis of the urogram.