Hypothesis / aims of study
The Liverpool and the Siroky male nomograms provide normal reference ranges for the maximum and average urine flow rates over a wide range of voided volumes (VV). These flow nomograms are the most common used in the evaluation of uroflowmetry (UF). Liverpool nomogram contains an age correction and uses voided volume, while Siroky nomogram employs bladder volume (voided volume plus post void residual urine). Aim of the study was to evaluate the concordance between Liverpool and Siroky nomograms in the analysis of uroflowmetry of young healthy male volunteers.
Study design, materials and methods
From January 2018 to January 2019 a group of young men, aged from 18 to 35 years, were enrolled as healthy volunteers in a prospective, multicenter study involving two urological Centers. Informed consent was obtained by all the volunteers. Exclusion criteria were: the presence of lower urinary tract symptoms (LUTS), urological and neurological diseases, previous surgery of the lower urinary tract, pelvis and genitalia, pharmacological therapies, pelvis’ radiation therapy, previous urethral catheterization. At baseline, all the subjects underwent detailed history and physical examination and the recording of the International Prostate Symptoms Score (IPSS) questionnaire. According to the severity of IPSS scores, subjects were divided into 3 groups: i), scores between 0-7; ii), scores between 8-19; iii), scores between 20-39. A VAS scale was used to assess subjects’ satisfaction on the voiding performance and the comparison with the usual voiding at home. All participants were asked to perform a uroflowmetry under a normal voiding desire. The examination was repeated only in case of voided volume lower than 150 ml or higher than 500 ml. All the uroflowmetry parameters, including maximum and average flow rate (Qmax-Qave), voided volume, time voiding and the shape of the UF, were recorded. Post-void urinary residual volume (PVR) was measured with a bladder scan immediately after performing UF. Uroflowmetry data were plotted both in Liverpool and in Siroky nomograms. Coefficient of age correction was considered for Liverpool nomogram. Bladder volume was used for Siroky nomogram. The comparison between the 2 nomograms on the uroflowmetry parameters and the relationship between UF parameters and IPSS and VAS scale scores were investigated. Statistical analysis was performed using T test and Mann-Whitney test and Cohen’s kappa statistic agreement.
Data was completed in 52 male volunteers. Pathological UF rate was 33.3% (18/52 subjects) using Liverpool nomogram, while according to the Siroky no pathological UF was found (Table 1). The concordance between nomograms in non-pathological subjects was 65.3% (34/52), while in pathological volunteers was 0% (18/0). The Cohen’s kappa statistic agreement was “0”, so “very scarce”. In table 2 are reported data of the groups divided according to Liverpool nomogram outcomes and the distribution of the subjects (pathological vs normal) according to the IPSS severity score. Statistically significant differences between the two groups were demonstrated in both mean and median Qmax, Qave, VV, voiding time, but not in PVR, IPSS total score and VAS.
Interpretation of results
Liverpool and Siroky nomograms are tools commonly used in the evaluation of UF. UF of the healthy male volunteers were assessed as normal using Siroky nomogram as expected. Surprisingly, in a third of the subjects non reporting LUTS and with normal UF at Siroky nomogram, a pathological UF was detected by the Liverpool nomogram. A statistical lack of agreement between the two nomograms was detected. The two nomograms are based on flow rate (Qmax and Qave) and urinary volumes (voided volume or bladder volume). Flow rate, both mean/median Qmax and Qave, was significantly lower in the group of subjects with pathological UF at Liverpool nomogram (16 ml/s vs 24 ml/s). Thus, this parameter may have had a critical impact on the results and may partially explain the different sensibility of the two nomograms. Another point could be that in the group of males with pathological UF at the Liverpool, the VV was higher causing an overstretching of the bladder muscle and lowering the flow rate. Mean/median voiding time was significant lower in subjects with pathological UF at the Liverpool, confirming a possible detrusor overstretching. Mean/median IPSS score was similar in the two groups, therefore lower urinary symptoms did not impact on the UF outcomes. The reported subjective evaluation of the flow was normal in all the volunteers; thus, the emotional condition may not have influenced the UF results. A limit of this study was that volunteers performed only one UF and repeated the examination only when VV was not appropriate with the inclusion criteria. Another potential limit was a limited number of males in the sample size. Anyway, this is an ongoing study, so further larger data may be helpful to confirm these findings.