Objective: To evaluate in a prospective study the effect of urethral instrumentation (flexible cystoscopy) on uroflowmetry, and in particular the peak urinary flow rate (Qmax).
Patients and methods: Thirty-two consecutive patients (median age 61.8 years, range 24-80) undergoing flexible cystoscopy were included in the analysis. Patients with active urethral stricture disease or urinary infection were excluded. The indications for cystoscopy included haematuria (44%), voiding symptoms (66%), history of bladder cancer (19%), and history of perineal trauma (3%). Patients underwent uroflowmetry immediately before instrumentation. The postvoid residual volume (PVR) was measured by bladder catheterization. After cystoscopy the bladder was completely emptied and then filled with the same volume of sterile normal saline (bladder volume = voided volume + PVR), and the patient underwent a second uroflowmetry.
Results: Patients with voiding symptoms (21, 66%) had a median (range) American Urological Association symptom score of 17 (4-34), a Bother score of 16 (1-23), and Quality of Life score of 3 (1-6). The mean Qmax was 16.9 (4.5-36.9) and 13.3 (4.5-39.4) mL/s before and after cystoscopy, respectively (P = 0.029). The mean percentage difference in Qmax was + 27 (- 23 to 139)% higher before than after cystoscopy. After cystoscopy, up to 25% (eight) and 21% (seven) patients had a lower Qmax, from > 15 to < 15 mL/s and from > 12 to < 12 mL/s, respectively. There were no significant differences in the bladder volume and PVR (P = 0.914 and 0.984, respectively).
Conclusions: Urethral instrumentation by flexible cystoscopy significantly alters Qmax. A 'false' mean change in Qmax (favouring improvement) of +27% would result if uroflowmetry data after instrumentation were used at baseline. Therefore, study protocols for benign prostatic obstruction should exclude uroflowmetry data obtained after urethral instrumentation; failure to exclude such data will lead to disproportionately greater improvements in Qmax that are independent of the therapy delivered.