Urine does not normally contain any significant numbers of micro-organisms. However, it can become contaminated from bacteria or yeasts introduced into the urinary tract. The resulting infection causes symptoms of pain or burning during urination (dysuria), frequency and a cloudy, offensive smelling urine.
Most urinary tract infections (UTI’s) are caused by Escherichia coli (E. coli). Other frequently identified bacteria are Proteus, Klebsiella, and Staphylococcus saprophyticus1.
Why send an MSU?
Once a mid stream urine (MSU) is obtained, the laboratory dudes are able to count the number of white blood cells (pus cells) or micro-organisms such as bacteria or yeast (colony count) under a microscope2. The presence of large numbers of these strongly suggest a UTI. Further tests are performed to ascertain antibiotic sensitivities ( This is often ordered as MC&S: Micro, culture and sensitivty )
The specimen is then incubated at body temp for 24hrs on agar plates and re-examined.
If the inoculated plates remain negative for significant growth the specimen culture is considered negative.
The theory is that by catching the mid section of the urine flow, you obtain a specimen that has not been contaminated by bacteria colonising the distal urethra and meatus as these are washed clear by the initial flow.
Logically, a stronger flow is going to provide a more effective ‘wash’, so the best time to obtain an MSU is when the bladder is full.
Why the fuss?
It is important to perform this procedure carefully so as not to contaminate the specimen, resulting in the lab dudes counting a ponderance of squamous epithelial cells whilst cursing the ineptitudes of the nurses on your ward.
Why the rush?
The specimen should be sent to the lab as soon as as possible (ideally within 30 min) after collection. Urine is an excellent culture medium for any bacteria or micro-organisms that are present. Especially if left standing in a warm environment. This can lead to false positive results.
If the specimen cannot be sent straight away it should be refrigerated at around 4 degrees celsius. At this temperature an accurate analysis can be made for up to 4-6 hours.
Collecting the sample:
- Ensure patient privacy and dignity throughout.
- Explain the procedure.
- Wash your hands.
- Don gloves and eye protection. Yup you read me. Speaking from personal experience here.
- Position patient on bedpan/toilet or position urinal.
- Using saline soaked gauze, separate labia or retract foreskin if present.
- Clean urethral meatus with 0.9% sodium chloride soaked gauze in a downwards motion FRONT TO BACK.
Cleaning of the genital area before collecting an MSU has been found to make little difference in contamination rates3, however, the principles of good hand and genital hygiene should be promoted anyways.
- Ask patient begin to pee into the toilet/bedpan/bottle
- Catch midstream specimen in sterile specimen container or sterile kidney dish taking care not to accidentally contaminate the specimen or touch the inside surfaces of the container.
- Allow patient to finish their pee.
- Label specimen correctly with patient’s name, clinical details and time and date of collection. (Note on the request form if the patient is menstruating).
- Make sure the lid is on tightly ( specimens that arrive at the lab outside their containers are not appreciated by the lab dudes. You do not want to anger the lab dudes) and place in biohazard collection bag.
If the patient is collecting the sample themselves, spend a little time to go over the process as above ( ‘cept they wont be needing gloves or eye protection) and highlight the importance of not contaminating the specimen.
A final word on the foreskin (if they have one).
If you have retracted the foreskin during this procedure, make sure to put it back where you found it.
Paraphimosis (also known as capistration) potentially occur if the foreskin has not been reduced after the procedure. Swelling of the glans makes reduction increasingly difficult and results in pain and potentially vascular compromise.
Paraphimosis is considered a urologic emergency that requires immediate dorsal slit or circumcision if the foreskin cannot be manually reduced’
I have even heard the sentence ‘gangrene of the penis’ bandied about. That would NOT be a good thing.
- Lab tests online [↩]
- laboratory dudes usually compensate for this sort of work by leading thrilling lives filled with skydiving and deep-sea free-diving and mixed martial arts when not crouched over their desks counting pus [↩]
- Leaver, R.B. (2007) The evidence for urethral meatal cleansing. Nursing Standard; 21: 41, 39–42. [↩]