Estimation of Residual Urine Volume with131I-Hippuran

Summary The use of 1311-Hippuran for the determination of the residual urine volume has been studied. It has been shown that a significant error is introduced into residual urine calculation by the small amounts of 1311-Hippuran which continue to be excreted in the urine for some hours after intravenous injection, even when renal function is good. The rise in activity over the bladder area appears to be linear with time in individual patients, but the slope is unpredictable. True residual urine volume can be calculated if readings of the activity in the bladder area and at the background site are taken at a short, measured interval after voiding, and again 30 minutes later. The use of such a corrective calculation has a number of practical advantages, and makes the determination more accurate. The activity measured over the umbilicus with the patient supine appears to give a satisfactory tissue background reading.