What is uroflow (urinary flow rate)?

From the Guidelines

Uroflow, or uroflowmetry, is a valuable diagnostic tool for evaluating patients with lower urinary tract symptoms (LUTS), particularly those with suspected obstructive or non-obstructive urinary issues, as stated in the 2021 AUA/SUFU guideline on adult neurogenic lower urinary tract dysfunction: diagnosis and evaluation 1.

Key Points to Consider

• Uroflowmetry measures the flow rate of urine during urination, providing insight into bladder function and bladder outlet function over time during a voiding event.
• The test is non-invasive, simple, and inexpensive, making it an attractive option for initial evaluation and ongoing monitoring of patients with LUTS.
• Abnormalities in uroflowmetry are indicative of a significant dysfunction in the voiding phase of micturition, guiding treatment decisions for conditions like benign prostatic hyperplasia, urethral strictures, or neurogenic bladder disorders.
• Normal results typically show a bell-shaped curve with maximum flow rates of 15-25 mL/second for men and 20-30 mL/second for women, though these values decrease with age.
• The 2012 AUA/SUFU guideline on urodynamic studies in adults recommends uroflow as a useful tool in the initial and ongoing evaluation of male patients with LUTS that suggest an abnormality of voiding/emptying 1.

Clinical Application

• Uroflowmetry can be used to differentiate between obstructive and non-obstructive urinary issues, helping clinicians to guide treatment decisions.
• The test can also be used for monitoring treatment outcomes and correlating symptoms with objective findings.
• The 2003 AUA guideline on management of benign prostatic hyperplasia suggests that uroflowmetry may be considered an optional diagnostic test for patients with LUTS, particularly those with complex medical histories or those desiring invasive therapy 1.

Limitations and Considerations

• Uroflowmetry has limitations, including its inability to distinguish between a low flow rate due to outlet obstruction, bladder underactivity, or both.
• The test depends on voided volume, which may result in significant variability of measurement in the same patient.
• False positives and negatives may lead to inappropriate treatment, highlighting the need for careful interpretation of results and consideration of additional diagnostic tests when necessary.

From the Research

Uroflow Studies

• The study 2 evaluated the effectiveness of tamsulosin in treating women with voiding difficulty and found significant improvements in voiding symptom score, storage symptom score, maximal flow rate, post-void residual urine, and voiding efficiency.
• In the study 3, tamsulosin was found to be associated with statistical reduction in overactive bladder symptoms in men, including reductions in voiding frequency, urgency scores, and nightly nocturia.
• The study 4 discussed the current clinical experience with tamsulosin, highlighting its effectiveness in treating lower urinary tract symptoms caused by benign prostatic hyperplasia, with rapid improvements in peak urinary flow rates.
• The study 5 compared the clinical efficacy of initial combined treatment of alpha-blocker plus anticholinergic agent to alpha-blocker monotherapy in benign prostatic hyperplasia patients with overactive bladder, finding significant improvement in storage symptoms with combined treatment.
• A meta-analysis 6 compared the clinical effectiveness and safety of alpha-blocker alone and combined alpha-blocker with an anticholinergic drug for bladder outlet obstruction with overactive bladder, finding that combined therapy was better than alpha-blocker alone, with significant reductions in total IPSS and storage IPSS.

Uroflow Parameters

• The study 2 found significant improvements in maximal flow rate in women with voiding difficulty treated with tamsulosin.
• The study 3 did not find baseline post-void residual or uroflow rate to be predictive of overactive bladder symptom improvement with tamsulosin in men.
• The study 4 highlighted the effectiveness of tamsulosin in improving peak urinary flow rates in men with lower urinary tract symptoms caused by benign prostatic hyperplasia.
• The study 5 found no significant differences in voiding IPSS and Qmax between combined treatment and alpha-blocker monotherapy in benign prostatic hyperplasia patients with overactive bladder.
• The meta-analysis 6 found no significant differences in Qmax between combined therapy and alpha-blocker alone for bladder outlet obstruction with overactive bladder.