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Background:The pressure-flow study (PFS) is considered the gold standard for the detection of bladder outlet obstruction (BOO) in men. However, several studies have raised the possibility that transurethral catheterization might have an obstructive effect on PFS while others did not.Objectives:To evaluate the effect of a 6 Fr transurethral catheter on the pressure-flow study and to evaluate its clinical implication in men.Materials and Methods:A retrospective chart review study of 515 men referred for an evaluation of lower urinary tract symptoms and who underwent an urodynamic study (UDS). Of those, 133 met our inclusion/exclusion criteria. Non invasive free-flow studies (NIFFS) were performed before every UDS. Cystometrogram and PFS were performed through a 6 Fr transurethral catheter.Results:The maximal flow rate (Qmax) was significantly higher (P < 0.001) in the NIFFS (15.0 mL/s (range 9.0-23.0)) than in the PFS (11.0 mL/s (range 7.0-18.5)). This difference became greater (18.5 mL/s (range 10.0-30.3) vs. 13.0 mL/s (range 6.0-25.0), in favor of the NIFFS) when we analyzed only the patients (n = 34) who voided a similar volume. According to the International Continence Society (ICS) nomogram, the use of the PFS alone would have resulted in the upstaging of 14% of cases (10/71) in the overall population and 24% (4/17) in the sub-analyzed group.Conclusion:A 6 Fr transurethral catheter significantly lowers the maximal flow rate by 4 mL/s. Its presence resulted in an upstaging on the ICS nomogram. However, further studies will be necessary to confirm this upstaging.

Objectives: Our objective was to evaluate the effect of a 6 Fr transurethral catheter on the uroflowmetry and to assess whether it potentially contributes to the bladder outlet obstruction (BOO) in women. Methods: We reviewed the charts of 1367 women who underwent an urodynamic study. We included patients with a non-invasive free-flow study (NIFFS) and pressure flow study (PFS) performed through a 6 Fr double lumen transurethral catheter. Results: In total, 120 women met the inclusion/exclusion criteria. Mean maximal flow rate (Q max ) was significantly higher (p < 0.001) in the NIFFS (27.2±11.1 mL/s) than in the PFS (19.3±10.6 mL/s). The mean difference between both Q max was 7.9±12.0 mL/s. Of these women, 92.3% (24/26) with a Q max <12 mL/s during PFS were found to have a Q max ≥12 mL/s during the NIFFS. Ten of the 72 women with an available P det. Q max were deemed to have a BOO according to the PFS and all of them had a Q max >12 mL/s during the NIFFS. Of the 10 patients, only 2 reported obstructive symptoms. Conclusion: The presence of 6 Fr transurethral catheters alters the PFS and results in a significant reduction of the Q max in patients who voided more than 250 mL. We believe that NIFFS should be performed in all patients before any urethral manipulation to lower a possible overdiagnosis of BOO and findings should always be correlated to clinical symptoms.

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