A midstream specimen of urine (MSU) is tested to look for infection.
What is the purpose of a midstream specimen of urine test?
- To confirm the diagnosis of a urine infection. The usual symptoms of a urine infection are pain when you pass urine, and passing urine frequently. However, symptoms are not always typical, particularly in children and the elderly, and a urine test is needed.
- To decide the best antibiotic to use. Some bacteria (germs) are resistant to some antibiotics. If the test shows that bacteria are in the urine then the bacteria are tested against various antibiotics. This finds which antibiotics will kill the bacteria in the urine.
How do I do a midstream specimen of urine?
The aim is to get a specimen (sample) of urine from the middle of your bladder. Urine is normally sterile (no bacteria present). If bacteria are found in the sample, it means that the urine is infected. A midstream sample is best as the first bit of urine that you pass may be contaminated with bacteria from the skin.
Prior to doing an MSU, wash your hands and genitals.
Women - hold open your labia (entrance to the vagina). Men - pull back your foreskin. Pass some urine into the toilet. Then, without stopping the flow of urine, catch some urine in a sterile bottle. (The bottle is usually provided by a doctor or nurse.) Once you have enough urine in the bottle, finish off passing the rest of your urine into the toilet.
Do not open the sterile bottle until you are ready to take the sample. You do not need to fill the bottle to the top, a small amount will do. (Some specimen bottles contain a preservative. If this is the case, a mark on the bottle will indicate the ideal amount of urine. However, if that is difficult, any amount is better than none.) Avoid touching any part of your genitals with the bottle, as this will increase the risk of contamination. Put the cap back on the container. The sooner the sample is given in to the doctor's surgery, or to the laboratory, the better. Within two hours is best. If that is not possible, put the sample in the fridge until you take it to the doctor or laboratory. The result of an MSU takes 2-3 days.
Urine specimens and children
It is not easy to get a pure MSU in young children and babies. The following methods get as good a sample as possible:
The usual way is to catch some urine in the specimen bottle whilst the child is passing urine. This is called the clean catch method. Just be ready with the open bottle as the child passes urine. (Be careful not to touch the open rim of the bottle with your fingers, as this may contaminate the specimen with bacteria from your fingers.)
One method is to place a special absorbent pad in a nappy. Your doctor or nurse will provide the special pad and tell you how to use it. Basically, when you place the pad in the nappy, check the pad every 10 minutes to see if it is wet with urine. Do not leave in for longer than 30 minutes as this may increase the risk of contamination. Therefore, replace the pad with a fresh one every 30 minutes until urine has been passed. Then, use the syringe provided to suck the urine from the pad. Then, transfer the urine in the syringe into a sterile container. Do not use other type of pads, cotton wool balls or gauze as they could alter the results.
If no pad is available, the following might work: take the nappy off about one hour after a feed. Tap gently with a finger (about once a second) just above the pubic bone. (This is the bone at the bottom of the abdomen above the genitals.) Have ready the open bottle. Quite often, within about five minutes, the baby will pass urine. Try to catch some in the bottle.
Further reading & references
- Liaw LC, Nayar DM, Pedler SJ, et al; Home collection of urine for culture from infants by three methods: survey of BMJ. 2000 May 13;320(7245):1312-3.
|Original Author: Dr Tim Kenny||Current Version: Dr Tim Kenny||Peer Reviewer: Dr Beverley Kenny|
|Last Checked: 19/07/2012||Document ID: 4297 Version: 38||© EMIS|
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