Variability of urodynamic parameters in patients with overactive bladder§


  • Conflicts of interest: Frenkl, T, Railkar R., Palcza, J., Scott, B.B., Alon, A. and Green S. are employees of Merck, Sharpe & Dohme Corp., A subsidiary of Merck & Co., Inc., the studies' sponsor, and may own stock/stock options in the company. Werner Schaefer declares no conflict of interest.

  • Ron van Mastrigt led the review process.

  • §

    The design of the study protocols was the responsibility of Merck Research Laboratories in collaboration with various health authorities. All analyses were conducted by scientists at Merck Research Laboratories. All authors had full access to the study data.



To report interpatient, intrapatient, and study site variability of urodynamic study (UDS) parameters in patients with overactive bladder (OAB).


Fifty-eight patients with OAB participated in a randomized, double-blind, placebo-controlled, urodynamic trial of an experimental OAB drug. Patients underwent 3 serial cystometries (CMGs) at three times: screening, pre-dose, and 4-hr postdose. This post hoc analysis describes intrapatient, interpatient, and site variability for the 6 CMGs prior to administration of study drug. Sites were given standard procedures for equipment calibration and UDS technique. Instilled volumes and pressures were recorded at first sensation of filling, first desire to void (FDV), strong desire to void (SDV), and maximum cystometric capacity (MCC).


The UDS volume endpoint with the smallest observed within-patient variability based on coefficient of variation (%CV) was MCC (%CV 24). Pressure measurements of all bladder sensations had larger within-patient variability than volume (MCC %CV 105). The between-patient variability was greater than within-patient variability for all bladder sensation volumes. Between-patient MCC variability for the 6 pre-treatment CMGs ranged from %CV of 50 to 58, whereas the within-patient %CV for MCC was 21–23. Excellent reproducibility was observed for bladder volume for MCC (intraclass correlation coefficients, range: 0.80–0.84). The between-site variability was large, as demonstrated by the mean volumes by site for MCC (132–397 ml).


MCC was the most reproducible sensation. Pressure measurements were substantially more variable than volume. Between-patient variability was substantially greater than within-patient variability. The observed intersite variability suggests that despite detailed instructions, sensations may not have been measured in a consistent manner across sites. Neurourol. Urodynam. Neurourol. Urodynam. 30: 1565–1569, 2011. © 2011 Wiley Periodicals, Inc.