MSU (Mid-stream Specimen of Urine)

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What is the purpose of an MSU 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.

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 'mid-stream' sample is best as the first bit of urine that you pass may be contaminated with bacteria from the skin.

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.) The sooner the sample is given in to the doctor's surgery, or to the 'lab', 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 'lab'. 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.

Young Children
The usual way is to catch some urine in the specimen bottle whilst in 'full flow'. 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.)

Babies
One method is to place a special absorbent pad in a nappy. Urine is sucked into a syringe from the wet pad. Another method is to use a plastic bag that sticks onto the skin and collects urine. If no pad or plastic bag 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 and catch some in the bottle.

© EMIS and PIP 2006   Updated: June 2006   PRODIGY Validated