Medical Content Created by the Faculty of the
Harvard Medical School
For a regular urinalysis, you are asked to urinate briefly into a plastic cup. When urine is collected for a urine culture, you must provide a "clean catch" sample - one that is not contaminated by skin cells and skin bacteria. This is so the doctor can obtain a sample of urine from inside your bladder, where normally there should be no bacteria. In contrast, there are many bacteria on the skin of a penis or in a vagina. The trick (harder for a woman than a man) is to pee directly into a sterile container without having the stream of urine first touch your skin or the nonsterile tissues of the vagina.
To collect a clean catch sample, you are given a sterile plastic container and asked to wipe off the area around your urethra (where urine exits) with an antiseptic cloth. For women, it's also helpful to hold the two labia (outer walls) of the vagina apart with one hand when you urinate, so that the stream of urine passes directly into the sterile container. Since the first flow of urine is most likely to be contaminated by bacteria from around the opening of the urethra, first urinate for a moment into the toilet and then use the cup to collect the "middle" portion of your urine stream.