Quantitative assessment of uroflow: is there a circadian rhythm?

OBJECTIVES To investigate if the circadian rhythm of urinary flow values varies within groups of patients with varying degrees of bladder outlet obstruction. METHODS A total of 170 patients with lower urinary tract symptoms suggestive of bladder outlet obstruction used a home-based uroflowmeter and produced a total of 1670 correctly measured flows at home. These patients also underwent a screening program with free urinary flowmetry in the hospital and a urodynamic pressure and flow study. RESULTS There is a circadian variability in urinary flow values in men with higher grades of obstruction. These men have a higher peak urinary flow with a smaller voided volume and thus a shorter flow time in the early afternoon when compared with late evening, early morning, and the midnight to morning periods. CONCLUSIONS This significantly greater maximum flow in the afternoon in men with higher grades of obstruction can be an important bias in studies where the primary end point is to assess a small improvement in maximum flow. Therefore, the circadian rhythm of uroflow has to be taken into account in the evaluation of the efficacy of treatment. Patients participating in clinical research studies should produce their urinary flow in the clinic always during the same time period, either in the morning or in the afternoon, and should not switch their appointment time.