A urine C&S is a urine culture and sensitivity test. It identifies the specific bacteria (or other germs) causing a urinary tract infection and then determines which antibiotics will effectively treat it. Unlike a basic urinalysis, which only flags signs of infection like white blood cells or cloudiness, a C&S pinpoints the exact organism responsible and tells your provider precisely which medication to prescribe.
How Culture and Sensitivity Work Together
The test has two distinct phases. In the culture phase, a lab technician places your urine sample on a substance that encourages germ growth. Bacteria typically grow within 24 to 48 hours, though fungi and other organisms can take longer. If nothing grows, the culture is negative, meaning there’s no active infection. If bacteria do grow, the lab identifies the specific type using a microscope or chemical tests.
Once the organism is identified, the sensitivity phase begins. The lab exposes those bacteria to a panel of different antibiotics to see which ones stop growth or kill the bacteria. Results come back in three categories:
- Susceptible: The antibiotic effectively stopped or killed the bacteria. It’s a good treatment choice.
- Intermediate: The antibiotic may work but could require a higher dose or more frequent dosing.
- Resistant: The antibiotic failed to stop the bacteria. It would not be effective as a treatment.
The full process, culture plus sensitivity testing, usually takes up to three days from when your sample reaches the lab.
Why Your Provider Ordered It
A C&S isn’t always necessary for a straightforward UTI. Providers often prescribe a common antibiotic based on symptoms alone for a first, uncomplicated infection. But certain situations call for the more detailed information a culture provides.
Your provider is more likely to order a urine C&S if you have a UTI that didn’t clear up after an initial round of antibiotics, recurrent infections, a kidney infection (pyelonephritis), or a history of drug-resistant urinary bacteria. It’s also standard during pregnancy: guidelines recommend at least one urine culture during pregnancy, even without symptoms, because untreated urinary bacteria can cause complications. Men with prostate-related urinary problems and patients with long-term catheters are other common candidates.
For people without any UTI symptoms, routine urine cultures generally aren’t recommended. Bacteria can live in the urinary tract without causing harm, a condition called asymptomatic bacteriuria, and treating it unnecessarily contributes to antibiotic resistance.
How To Collect the Sample
Most urine C&S tests use a “clean catch” midstream sample. The goal is to avoid contaminating the specimen with bacteria from your skin, which would muddy the results. If possible, collect the sample when urine has been sitting in your bladder for two to three hours.
Start by washing your hands. If you have a vagina, use the provided sterile wipes to clean between the labia, wiping front to back, then clean around the urethral opening. If you have a penis, wipe the tip with a sterile wipe (pull back the foreskin first if uncircumcised). Begin urinating into the toilet, then catch the midstream portion in the cup until it’s about half full. Finish in the toilet. Screw the lid on without touching the inside of the cup.
For infants, a special adhesive collection bag is placed over the genital area. Active babies sometimes dislodge the bag, so you may need more than one attempt. Once collected, return the sample promptly. If you’re at home, refrigerate it in a sealed plastic bag until you can bring it in.
Reading Your Results
A negative culture means no significant bacterial growth was detected. A positive culture identifies the specific organism and reports its concentration in colony-forming units per milliliter (CFU/mL). The standard threshold for a urinary tract infection is 100,000 CFU/mL or higher. Counts below that level may represent contamination or colonization rather than true infection, depending on your symptoms.
The most common bacterium found in positive urine cultures, by a wide margin, is E. coli. It causes the majority of both simple and complicated UTIs. Other organisms that show up regularly include Klebsiella pneumoniae, Proteus mirabilis, Enterococcus faecalis, and Staphylococcus saprophyticus.
If your results say “mixed flora,” it usually means three or more types of organisms were present, which suggests the sample was contaminated during collection rather than reflecting a true infection. Your provider will likely ask you to repeat the test with a fresh sample. Similarly, a result showing more than two organisms raises the possibility of contamination and may not be usable for diagnosis.
What Happens After Results Come Back
If you were already started on an antibiotic before the results arrived, the sensitivity report serves as a check. If the bacteria turn out to be resistant to what you’re taking, your provider will switch you to one that tested susceptible. If you weren’t yet treated, the results guide the initial prescription directly.
This targeted approach is one of the main advantages of a C&S over guessing with a broad-spectrum antibiotic. It reduces the chance of treatment failure, limits unnecessary antibiotic exposure, and helps combat the growing problem of drug-resistant bacteria. For people with recurrent UTIs or infections that keep bouncing back despite treatment, the sensitivity report is especially valuable because it reveals exactly which medications their particular strain of bacteria will and won’t respond to.