Definition & Overview
A urinary bladder residual study refers to various tests used to measure residual urine volume. This is the amount of urine left in the bladder after a person urinates. It is measured using a bladder scan or a post-void residual (PVR) urine test.
A urinary bladder residual study is used to determine if a person can empty his bladder completely. If not, it could be a sign that he is suffering from urinary problems.
The procedure is part of urodynamic testing that patients undergo to assess the health of the bladder and the urethra. This test is performed by urologists, gynaecologists, internal medicine specialists, and primary care physicians. Its goal is to diagnose urinary problems and help doctors determine the best treatment for the patient.
Who Should Undergo and Expected Results
A urinary bladder residual study is beneficial for patients who are suspected of having urinary problems. These tests can help diagnose:
- Enlarged prostate or benign prostatic hyperplasia
- Urinary retention
- Neurogenic bladder dysfunction
Potential causes of urinary retention include:
- Impaired bladder contractibility
- Bladder outlet obstruction
- Lack of coordination between bladder contractions and sphincter relaxations
- Multiple sclerosis
- Parkinson’s disease
- Severe faecal impaction
- Neurogenic bladder
- Bladder denervation due to pelvic surgery
Patients are usually advised to undergo a urinary bladder residual study when they experience the following symptoms:
- Increased or abnormal urinary frequency
- Inability to completely empty the bladder during urination
- Abdominal distention
Patients who suffer from urinary problems should undergo testing to receive a diagnosis and to address the problem. When left untreated, the condition can lead to complications, such as urinary tract infection and obstructive uropathy. The test is also performed on patients who suffer from a spinal injury that may have affected their micturition reflex.
The normal result of a urinary bladder residual study is less than 50 mL. If the number is greater, this means that the patient cannot void or empty his bladder completely.
Before making a diagnosis, the results of the test are cross-referenced with the patient’s voiding frequency. If a patient’s residual urine volume is up to 100 mL, but goes to the toilet every 2 hours, the results are considered acceptable. If the voiding frequency is greater than 2 hours but the patient does not experience frequent urinary tract infections, this may still be acceptable in most cases. However, if the patient is prone to or is experiencing lower urinary tract symptoms, the residual volume should be lower.
An abnormal residual urine volume may prompt doctors to prescribe other tests, such as:
- Blood test
- Ultrasound scan
- Urodynamic testing
How is the Procedure Performed?
A urinary bladder residual study is performed using a post-residual void (PVR) test. The test is part of the urodynamic testing performed on patients showing symptoms of urinary problems. There are two ways to perform this test:
- Straight catheter post void residual - This test measures residual urine by draining the bladder completely with a catheter after the patient goes to the bathroom. The collected residual urine in the catheter is then measured.
To perform the procedure, the patient is asked to go to the bathroom to urinate. He is then asked to lie flat on an exam table before a thin flexible catheter is inserted about 2 inches into the bladder. This may cause some discomfort or a slight burning sensation.
- Ultrasound post void residual - This alternative method measures residual urine using ultrasound scanning. After using the bathroom, the patient is asked to lie flat on an exam table. His lower abdomen and pelvis are then exposed. The technician then performs an ultrasound scan by applying gel on the patient’s abdomen and placing the ultrasound probe over the area. The probe, with the help of the gel, makes a recording of the inside of the abdomen.
Both methods do not require special preparation from the patient. Patients can also resume their normal activities immediately after the procedure.
Possible Risks and Complications
A urinary bladder residual study that uses catheters comes with certain risks. These include infection and injury to the urethra.
However, when done carefully, this method is quite safe. It is the preferred method because it is less expensive than an ultrasound.
An ultrasound scan also comes with its own risks, such as exposure to small amounts of radiation.
McNeill SA, Hargreave TB, Geffriaud-Ricouard C, Santoni J, Roehrborn CG. “Postvoid residual urine in patients with lower urinary tract symptoms suggestive of benign prostatic hyperplasia: pooled analysis of eleven controlled studies with alfuzosin.” Urology. 2001 Mar; 57(3): 459-65. https://www.ncbi.nlm.nih.gov/pubmed/11248620
Brookman-May S, Burger M, Hoschke B, Wieland WF, Kendel F, Gilfrich C, Braun KP, May M. “Association between residual urinary volume and urinary tract infection: prospective trial in 225 male patients.” Urologe A. 2010 Sep; 49(9): 1163-8. https://www.ncbi.nlm.nih.gov/pubmed/20717648