World J Urol (2009) 27:747–753 strong desire to void and a pressure-Xow study followed. After the voiding phase, postvoid residual urine volume was measured via the transurethral catheter and the bladder was once more checked for emptiness with the conven- tional ultrasound array. The urodynamic investigation was repeated immediately afterwards exactly as described above and ultrasound BWT measurements were performed during the second cystome- try at 150 and 250 ml again (BS150B and US150B; BS250B and US 250B). All measurements were performed by a single experienced urologist ( . .). Statistical evaluation Repeatability of each BWT measurement method from rep- licated measurements at both bladder Wlling volumes sepa- rately was assessed with the methodology described by Bland and Altman [15]. For each method and at each spe- ciWc bladder Wlling volume, the distribution of diVerences between replicate measurements was plotted against their average. The existence of any systematic diVerence between replicates, their variation (indicated by mean § 2SD), and any possible trend of the distribution of diVerences across the range of BWT measurements was assessed graphically. Only patients with two valid measure- ments were included in the analysis. In order to compare the two diVerent methods of BWT measurement at each bladder Wlling volume separately, and to determine the agreement between them, the same methodology was applied based on valid measurements by both modalities during the Wrst urodynamic investigation only. The one- sample t test was applied to test whether mean diVerences between replicates diVered from zero. McNemar’s test was used to compare the proportions of patients with valid mea- surements by the same modality at diVerent bladder Wlling volumes and the proportions of patients with valid mea- surements by diVerent modalities at the same bladder Wlling Table 1 Characteristics of patients who participated in the prospective study The patients sought help for lower urinary tract symptoms, urinary incontinence, or postvoid residual urine and were randomly selected regardless of age, body-mass index, or urodynamic diagnosis PVR postvoid residual urine 749 volume. A probability of 0.05 or less (two-tailed) was con- sidered to indicate statistical signiWcance. The data were analyzed with SPSS (version 15.0; Chicago, IL, USA). Results Fifty unselected patients aged 21–86 years (median: 62.5 years; men/women: 30/20) submitted to urodynamic investigation were included in the study. Patient character- istics are summarized in Table 1. All patients reached the bladder Wlling volume of 150 ml during cystometry but only 47 patients reached 250 ml. Valid BWT measurements with US could be performed during both urodynamic investigations in all 50 patients at 150 ml and all 47 patients at 250 ml. In contrast, BS failed to deliver a valid measurement after central server evalua- tion in four patients (8%) during the Wrst and seven patients (14%) during the second measurement at 150 ml. The same happened at 250 ml in one (2.1%) and three patients (6.4%) during the Wrst and second cystometry, respectively. The proportion of patients with valid measurements by each modality at 150 ml did not diVer signiWcantly in the Wrst urodynamic investigation (p = 0.125), but was signiWcantly higher for US in the second urodynamic investigation (p = 0.016). The proportions did not diVer signiWcantly at 250 ml (Wrst/second urodynamic investigation: p = 1.0/ 0.25). No signiWcant diVerences in patients with valid mea- surements were detected between 150 and 250 ml bladder Wlling volumes for BS in either urodynamic investigation (Wrst/second urodynamic investigation: p = 0.375/0.125). Comparison between ultrasound measurements obtained by the same method BWT measurement values using US (BS) ranged from 1.1 to 13.5 mm (1.8–6.1 mm) at 150 ml and from 1.2 to All patients (n = 50) Men (n = 30) Women (n = 20) Age (years) Median (range) Body-mass index (kg/m2) Median (range) Primary urodynamic diagnosis Detrusor overactivity § incontinence Stress urinary incontinence Increased bladder sensation Bladder outlet obstruction Detrusor underactivity Dysfunctional voiding and PVR 62.5 (21–86) 26.0 (19.1–40.3) 10 9 4 17 8 2 65.0 (32–86) 26.0 (19.1–36.1) 6 0 1 17 6 0 54.5 (21–78) 26.1 (19.5–40.3) 4 9 3 0 2 2 123