Variability in urinary flow rate and prostate volume: an investigation using the placebo arm of a drug trial

Abstract

Purpose: We analyzed a large data set to study reproducibility of peak urinary flow rates and prostate volumes in benign prostatic hyperplasia patients.

Materials and methods: Longitudinal data were analyzed from 284 placebo treated patients in a double-blind, placebo controlled benign prostatic hyperplasia drug trial.

Results: A statistically significant increase in mean maximum flow rate was seen in the initial 3 measurements, as well as after adjusting for voided volume and time between uroflows. The mean maximum flow rate increased from 8.61 to 9.36 ml. per second at measurement 4 (8.7%). Of the patients 43% had 2 consecutive prostate volume determinations within +/- 10%. Within patient variability accounted for 7% of total prostate volume variability.

Conclusions: With subsequent voidings maximum flow rate increases in a large group of patients. At least 4 uroflows must be performed to reach a plateau for maximum flow rate. Explanations for this finding may be the increasing experience of the patient and regression to the mean. These findings may impact on comparison of large trials of treatment efficacy. Within patient variability of prostate volume is substantial and, in addition to measurement method and lack of reader blinding to time and patient identity, may be caused by other yet unknown factors.