Standing or Sitting to Void? Comparative Uroflowmetry in Healthy Male Volunteers: A Randomized Crossover Study with Equivalence Analysis.

Abstract

Introduction: The posture adopted during voiding may influence uroflowmetric parameters, such as maximum urinary flow rate (Qmax), voided volume, and time to maximum flow (tQmax). Published studies have shown inconsistent results, and uncertainty persists regarding the clinical relevance of these differences in healthy men.

Objective: To compare uroflowmetric parameters during standing and sitting voiding in healthy male volunteers using a randomized crossover design, incorporating a formal equivalence analysis (Two One-Sided Tests, TOST) for the primary outcome (Qmax).

Material and methods: This prospective, randomized, 2 × 2 crossover study included 52 healthy male volunteers allocated to the sitting → standing (n = 24) or standing → sitting (n = 28) sequence, with a minimum washout period of 24 h. The primary outcome was Qmax and the secondary outcomes were the total voided volume and tQmax. Paired tests, correction for multiple comparisons (Bonferroni and Benjamini-Hochberg), linear mixed-effects models, Bayesian analysis, and TOST equivalence analysis for Qmax (margin ±2.5 mL/s) were used.

Results: Baseline characteristics were comparable between sequences. No significant differences between postures were observed for Qmax (Δ = -1.47 mL/s; 95% CI -3.55 to 0.62; p = 0.164) or for total volume (Δ = -14.7 mL; 95% CI -43.9 to 14.6; p = 0.318). The tQmax was longer while standing (Δ = +3.32 s; 95% CI 0.94 to 5.69; p = 0.011), remaining significant after Bonferroni correction (p = 0.031) and FDR correction (q = 0.031). The mixed models did not identify either sequence or period effects. Bayesian analysis showed moderate evidence in favor of a difference in tQmax (BF₁₀ = 4.99) and in favor of no difference in volume (BF₀₁ = 4.10). The equivalence analysis (TOST) for Qmax was not significant (p-TOST ≈ 0.16); therefore, the equivalence of the maximum flow between postures could not be formally claimed with the present sample size.

Conclusions: In healthy men, voiding posture did not significantly modify the maximum urinary flow rate or voided volume; however, formal equivalence of Qmax was not demonstrated. The sitting position was associated with a shorter time to maximum flow, a small difference that is unlikely to be clinically meaningful and was partly dependent on a single outlier. Larger, pre-registered studies with pre-specified equivalence analyses and symptomatic populations are required.