The test is used to diagnose a urinary tract infection (UTI).

A urine culture may be ordered when symptoms indicate the possibility of a urinary tract infection, such as pain and burning when urinating and frequent urge to urinate. Antibiotic therapy may be prescribed without requiring a urine culture for symptomatic young women, who have an uncomplicated lower urinary tract infection. If there is suspicion of a complicated infection, or symptoms do not respond to initial therapy, then a culture of the urine is recommended. Pregnant women without any symptoms may be screened for bacteria in their urine, which could affect the health and development of the fetus.

The presence of a single type of bacteria growing at high colony counts (greater than 10,000 colony forming units (CFU)/ml) is considered a positive urine culture. A culture that is reported as no growth in 24 or 48 hours or less than 10,000 CFU/ml usually indicates that there is no infection. If the symptoms persist, however, the culture may be repeated to look for the presence of bacteria at lower colony counts (less than 10,000 CFU/ml) or other microorganisms that may cause these symptoms. The presence of white blood cells and low numbers of microorganisms in a symptomatic patient is a condition known as acute urethral syndrome.

If a culture shows growth of several different types of bacteria, then it is likely that the growth is due to contamination. This is especially true if the organisms present include Lactobacillus and common nonpathogenic vaginal bacteria in women. If the symptoms persist, the doctor may request a repeat culture on a sample that is more carefully collected.

The presence of a significant amount of a single type of bacteria usually indicates an infection. Susceptibility testing is performed to guide antimicrobial treatment. Any bacterial infection may be serious and can spread to other areas of the body if not treated. Since pain is often the first indicator of an infection, prompt treatment, usually with antibiotics, will help to alleviate the pain.

Females get UTIs more often than males. Even school-age females may have frequent UTIs. For males with a culture-proven UTI, the doctor may order further tests to rule out the presence of a kidney stone or structural abnormality that could cause the infection.

If you have recurrent urinary tract infections, culture and susceptibility testing may be performed with each episode. For patients who have frequent UTIs, their bacteria may become resistant to antibiotics over time, making careful selection of antibiotic (and the full course of treatment) essential. Those with kidney disease and/or with diseases that affect the kidneys, such as diabetes and those with compromised immune systems, may be more prone to recurring UTIs.