MAXIMUM URINARY FLOW-RATE BY UROFLOWMETRY - AUTOMATIC OR VISUAL INTERPRETATION

We measured the maximum urinary flow rate monthly for 1 year by uroflowmetry in 1,645 patients in a double-blind, placebo-controlled study of finasteride therapy for benign prostatic hyperplasia. Patients were randomized to receive placebo (555) or finasteride (1,090). A total of 23,857 flow measurements was obtained. Because of the presence of artifacts on many uroflow curves, we read the maximum urinary flow rate values manually and compared them to the values provided electronically by the uroflowmeter. On average, the manually read values were 1.5 ml. per second lower than the machine read values. Artifacts causing a difference of 2 ml. per second or more between the 2 methods were found in 20% and of more than 3 ml. per second in 9% of the tracings. The difference between treatment groups in mean maximum urinary flow rate change at the end of the study was the same with both reading methods. However, confidence intervals were 15 to 25% larger for the machine read compared to the manually read values. This larger variability in machine read maximum urinary flow rate has a marked negative impact on the power of statistical tests to assess any given difference in maximum urinary flow rate between treatment groups. Furthermore, it increases sample size requirements by 50% to achieve any given statistical power. We conclude that maximum urinary flow rate artifacts contribute significantly to the variability of maximum urinary flow rate measurement by uroflowmetry. Manual reading of the maximum urinary flow rate eliminates an important fraction of such variability.