The day-to-day variation (test-retest reliability) of residual urine measurement

To determine the variation in repeated measurements of post-void residual urine volume (PVR), determined by transabdominal ultrasonography (TAUS), within an individual over time (test-retest reliability).

Forty men with symptomatic benign prostatic hyperplasia and awaiting transurethral resection of the prostate were studied over 3 months. Each underwent TAUS to determine both pre- and post-micturition residual volumes on six occasions within the study period.

Although one-third of the patients had approximately constant residual volumes (variation in range < 120 mL), two-thirds had wide intra-individual variations over time (variation in range 150-670 mL). The values were log transformed to give a normal distribution and subjected to analysis of variance; there was a wide variation between and also within individuals. The larger the mean PVR, the larger was the overall variation in time. For those with a mean PVR of < 100 mL, the variation was less marked and these patients showed a more consistent test-retest repeatability.

Although the PVR determined by TAUS may be useful to indicate aspects of bladder dysfunction or outlet obstruction, the wide variation in repeated measurements in the same individual limits its use for any clinical purpose that requires repeated assessment, e.g. in monitoring the response to treatment. There is poor test-retest reliability and PVRs cannot be determined reliably from a single measurement.