Chris Winters led the review process.
Original Clinical Article
Article first published online: 29 SEP 2010
Copyright © 2010 Wiley-Liss, Inc.
Neurourology and Urodynamics
Volume 30, Issue 1, pages 52–57, January 2011
How to Cite
Burton, C., Weiss, J. P., Parsons, M., Blaivas, J. G. and Coats, A. C. (2011), Reference values for the nocturnal bladder capacity index. Neurourol. Urodyn., 30: 52–57. doi: 10.1002/nau.20924
Conflicts of interest: none.
- Issue published online: 22 DEC 2010
- Article first published online: 29 SEP 2010
- Manuscript Accepted: 22 FEB 2010
- Manuscript Received: 11 NOV 2009
- bladder capacity;
- bladder diary;
- frequency–volume chart;
The Nocturnal Bladder Capacity Index (NBCi) has been reported to be useful in distinguishing between nocturia caused by low bladder capacity and nocturnal polyuria. This paper aims to calculate reference values for NBCi from an asymptomatic population by comparing these with NBCi values from patients with lower urinary tract symptoms (LUTS) to obtain an indication of the sensitivity with which the NBCi detects low nocturnal bladder capacity. This paper also compares the sensitivity of rounded and unrounded calculations of NBCi.
Computer processed 3-day bladder diaries from 253 asymptomatic volunteers and 184 female patients with LUTS were analyzed. NBCi values were calculated from each diary using rounded and unrounded formulae. 90th and 95th centile NBCi cutoff values were obtained from frequency distributions.
NBCi reference values from the asymptomatic group were 1.1 (unrounded) and 0.7 (rounded) for 90th centile, and 1.3 (unrounded) and 1.0 (rounded) for 95th centile. The use of the rounded formula gave identical NBCi values despite a large variation in Vn/Vmax ratios whereas unrounded NBCis varied continuously with Vn/Vmax ratios. The unrounded formula found significantly more elevated NBCis in the patient group.
We suggest that an unrounded NBCi of 1.3 be considered a cutoff point above which reduced nocturnal bladder capacity should be investigated as a cause of nocturia. Rounding the NBCi lead to an underestimation of elevated values in a population of female patients with LUTS. Neurourol. Urodynam. 30:52–57, 2011. © 2010 Wiley-Liss, Inc.