Water and dissolved substances like salt and potassium make up urine. It also contains creatinine, which is produced when muscle breaks down, and urea, which is produced when protein breaks down. Typically, urine contains certain concentrations of these waste materials. It can be an indication of a specific disease or condition if these concentrations are outside of the normal range or if other compounds are present. A straightforward lab test that determines what is in your urine is a 24-hour urine collection. The test evaluates kidney performance. Your urine is collected over the course of a full 24 hours and stored in a designated container or containers. Until the urine is brought back to the lab, the container(s) must be kept refrigerated.