Pressure changes in the dilated upper urinary tract on perfusion at varying flow rates.

The conventional Whitaker test assesses the pressure response to a constant perfusion rate of 10 ml/min. Twenty-eight kidneys were perfused at increasing flow rates up to 20 ml/min. Nine became obstructed at rates of 12 to 20 ml/min. The feasibility of such a high urine output has been tested and confirmed. The standard Whitaker test may therefore miss some cases with potentially obstructive hydronephrosis, the effects of which may be deleterious to renal function.