Usefulness of a prevoiding transabdominal sonographic bladder scan for uroflowmetry in patients involved in clinical studies of benign prostatic hyperplasia.

OBJECTIVE

Flow rate measurements in clinical studies require an amount of voided urine greater than 125 to 150 mL. Often patients do not void sufficient amounts of urine, and having them produce repeated flows is often difficult. Transabdominal sonographic scanning of the bladder is a simple method for estimating bladder volume. We determined by sonography the prevoiding bladder volume needed to void a sufficient amount of urine.

METHODS

Sixty-seven patients with a mean age +/- SD of 67.5 +/- 8.0 years underwent free flow rate measurement. Bladder volume was measured by transabdominal sonography when the patient had the sensation to void and after uroflowmetry to calculate residual urine.

RESULTS

The voided volume was 220 +/- 127 mL; the postvoiding residual urine volume was 92 +/- 88 mL; and the bladder scan volume was 309 +/- 158 mL. Among all patients, 23.9% had insufficient voided volumes of less than 125 mL in the flow rate measurements, and 31.3% had voided volumes of less than 150 mL. There was a strong correlation between the prevoiding measured volume and the voided volume (r = 0.836; P < .0001). Linear regression analysis of the flow rate recording yielded the following formula: voided volume = 11,766 + (0.673 x prevoiding volume).

CONCLUSIONS

Bladder scanning before uroflowmetry is a useful test for reducing the amount of nonevaluable flow rate data. If a voided volume of greater than 125 mL (>150 mL) is required, the mandatory prevoiding bladder scan volume should be greater than 200 mL (>250 mL), which would decrease the number of noneligible flow rate recordings from 23.9% to 4.5% (31.3% to 4.5%).