The midstream specimen of urine, or MSU, test is used to determine if someone has an infection. It can be used to test urinary tract health.
The MSU test is designed to get a sample of urine from the middle of the bladder. Urine does not contain any bacteria so if the sample does contain some, it means that there is an infection. The first stream of urine can have residual amounts of bacteria in it due to contact with the skin, which is why MSU tests are preferred.
The resulting urine sample from an MSU test can also be tested to determine which antibiotics should be taken by the patient in order to treat the bacterial infection.