A urine culture is indicated in individuals who have symptoms of a urinary tract infection: a compelling need to urinate, often with pain and blood in the urine, sometimes with back pain or fever in the case of more severe urinary tract infections. A culture can also be ordered after a routine urine test comes back positive for bacteria and nitrites, even in the absence of symptoms. A urine culture tests for the most common bacteria and yeasts after culturing for 24 or 48 hours. The sample collection technique is particularly important, to ensure that the identified organisms actually originated from the urinary tract and not from urethral or vaginal contamination. Typically, only one type of bacteria will be present in significant quantities after culturing. If more than two types of microorganisms are present, it may be an infection with multiple pathogens, but more often it will be the result of specimen contamination.
A result that shows no growth after 24 or 48 hours is generally consistent with no urinary tract infection. If symptoms persist, a urine culture should be repeated on another sample to identify the bacteria that were present in small amounts in the original collection or, upon request by the ordering physician, to look for other microorganisms that could be causing the symptoms.