How to collect a urine sample for testing?
Urine examination is commonly done as a part of a routine health check-up or to identify a specific condition related to the urinary tract or kidneys (urinary tract infection, blood in urine, or protein loss in urine). The best way to collect the urine sample for different indications to give accurate results will be explained below.
Urinary tract infection
The urine sample which is collected to evaluate for the identification of urinary tract infection should have minimal contamination by the bacteria which are normally present in the genital areas (distal urethra and genital mucosa). The sample collected should also represent the bacterial count in the bladder accurately.
Timing:
The urine sample collected while passing the first urine on awakening will have the highest possibility of detecting the bacterial infection. This is because bacteria in the bladder will have time to multiplicate in the urine overnight and the urine will be concentrated. At least for 4 to 8 hours urine should be in the bladder to demonstrate reliable bacterial growth. This way of collecting urine samples is not always possible as many a time we give the sample when we go to the doctor or lab for testing. The sample given later in the day will have a less bacterial count because of the dilute urine and washout while urinating previously during the day. Second voided urine in the day will serve the purpose for patients who are not in the hospital.
Method to collect urine:
“clean-catch” and “mid-stream” are the words used to explain the method of urine collection for urinary tract infection testing.
- Foreskin of penis is pulled back in males and labia in females are spread
- Washing is done with water and wiped dry
- Now the urine should be passed. The initial stream of urine is to be discarded because it flushes the contents of the urethra. After the initial part of urine is discarded then the stream of urine which is next called midstream urine is collected in the sterile container provided.
Handling of the sample:
Once the urine is collected for a urine culture to identify UTI, it has to be sent to the lab immediately. This is because bacteria in the urine if present will multiplicate and will give results with increased bacterial counts. If we are unable to take the sample to the lab immediately it has to be stored in the refrigerator at 4-degree Celsius. While taking the sample to the lab, the urine container should be kept in a bag or container with cold water or ice cubes until it is delivered to the laboratory. Keeping at a cold temperature prevents the bacteria from multiplicating and increasing in number.
Complete urine examination (CUE)
Complete urine examination includes chemical analysis by dipstick examination and microscopic examination to look for cells and casts in the urine. For random CUE, 1 to 2 hours stay of urine in the bladder is enough for proper assessment. The method of collection of urine for CUE is the same as that for urine culture (to identify urinary tract infection) explained above because the same urine sample may be used to do a microscopic examination, chemical analysis, and urine culture.
24-hour urine collection
24-hour urine is collected commonly to measure protein loss per day in the urine. The whole of urine should be collected during the 24 hours without fail. The amount of urine collected each time does not matter. Our aim is to collect the whole of the urine during the 24-hour duration. Following are the steps to collect the urine in 24 hours.
- Once we wake up in the morning pass the urine for the first time and flush it in the toilet. Note down the time (example: 7.15am). From this time point we should collect whatever urine we pass in the next 24 hours.
- Collect the urine in the container provided by the lab and store at room temperature or in the refrigerator.
- In between while passing stools (feces) the urine passed should also be collected in the container. Avoid contamination with feces in the container.
- Next morning, we should finish the sampling collection by collecting the first morning urine we pass. This last sample collection should be around the same time we initiated collection the previous day (between 7.05am to 7.20am).
Precautions to be taken
- Sexual intercourse should be avoided one day prior as it will increase cells and protein in the urine
- Menstrual blood during periods may contaminate the urine in females resulting in presence of red blood cells in the urine.
Dr Kishore Kumar Ariga
Nephrologist and renal transplant physician