Urine Culture: Understanding Your Report

Section Editor: Rodney E. Rohde PhD
June 3, 2026

A urine culture is a laboratory test that checks whether microorganisms, usually bacteria, are growing in your urine. Microorganisms (also called microbes) are living things too small to see without a microscope. The test is most often used to find out whether you have a urinary tract infection (a UTI), and, if something grows, to identify it and test which antibiotics are likely to stop it. An antibiotic is a medicine used to treat infections caused by bacteria.

This article explains what a urine culture report shows, what the different results mean, and what to ask your doctor, so you can better understand a report you have received. In most cases, a result of “no growth” or “no significant growth” is reassuring, while a high amount of a single type of bacteria points to a true infection.

What is a urine culture, and why is it done?

The urinary tract includes the kidneys, the bladder, and the tubes that connect them and carry urine out of the body. An infection of the bladder is called cystitis, and an infection that reaches the kidneys is called pyelonephritis. Together, these are known as urinary tract infections.

A urine culture is ordered when a UTI is suspected, often because of symptoms such as burning with urination, a frequent need to urinate, or pain. The test answers two questions: whether a microorganism is causing an infection, and which medicine is most likely to treat it.

Urine culture versus urinalysis

A urine culture is often done alongside a urinalysis, and the two are easy to confuse. A urinalysis is a quick screening test that examines urine using chemical strips and sometimes a microscope. It can give early clues that point toward infection, such as white blood cells (cells of the immune system), nitrites (a chemical some bacteria produce), or leukocyte esterase (a substance released by white blood cells). A urinalysis is fast but does not identify the exact microorganism. A urine culture is a test that grows bacteria so they can be identified and tested against antibiotics. The two tests work together: the urinalysis suggests whether an infection is likely, and the culture confirms it and guides treatment.

How the test is performed

Most urine samples are collected as a “clean-catch midstream” sample, meaning the area is cleaned first, and the sample is taken partway through urination. This step matters because it reduces the chance that harmless skin bacteria get into the sample. Sometimes urine is collected through a thin tube called a catheter. The sample is then placed in the laboratory under conditions that promote microbial growth. If something grows, it is identified and, in most cases, tested against antibiotics. A preliminary result is often available after about a day, and a final result after about two days.

How to read your urine culture result

The first part of your report describes what grew, if anything. You may see any of the following.

No growth, or no significant growth — No microorganisms grew, or the amount was too small to suggest an infection. For many tests, this is the expected, reassuring result.
A named microorganism with a colony count — If something grew, the report names it, for example, Escherichia coli (often written E. coli), the most common cause of UTIs. The report also gives an amount, measured in colony-forming units per milliliter (CFU/mL), which is explained in the next section.
Mixed flora, or mixed growth — Several different microorganisms grew in small amounts. This often means the sample picked up harmless bacteria from the skin during collection, rather than a single cause of infection.
Possible contaminant — When the laboratory suspects that bacteria entered the sample during collection, it may describe the result as a possible contaminant, meaning it may not reflect a true infection.

Colony counts and what they mean

The colony count, expressed as CFU/mL, estimates the number of microorganisms present. A colony-forming unit is the number of microorganisms that can grow into a visible cluster, called a colony, in the laboratory.

In general, a high count of a single bacterial type, often around 100,000 CFU/mL (10⁵) or more, indicates a true infection, while low counts or multiple different bacteria more often suggest contamination. These numbers are not firm cutoffs, however. A lower count can still be meaningful when you have clear symptoms, when the sample was collected through a catheter, or with certain bacteria. This is one reason your doctor reads the colony count alongside your symptoms rather than on its own.

Antibiotic susceptibility results

When a microorganism grows in a meaningful amount, the laboratory tests how well different antibiotics stop it. This is called antibiotic susceptibility, or sensitivity, testing. Each antibiotic is usually given a result of susceptible (likely to work), intermediate (may work, often at a higher dose or in certain conditions), or resistant (not expected to work). Some reports also include a number called the minimum inhibitory concentration (MIC). How to read these results is explained in detail in the article on culture and sensitivity testing.

When a positive culture does not need treatment

It is possible to have bacteria in the urine without having any symptoms of a UTI. This is called asymptomatic bacteriuria, and in most people it does not need treatment because treatment provides no benefit and can contribute to antibiotic resistance. There are important exceptions: bacteria in the urine are usually treated during pregnancy and before certain urinary tract procedures, even without symptoms. This is one reason a positive culture is always interpreted together with how you feel.

What happens after this test

A urine culture describes what was found and informs the decisions you and your healthcare team make together, rather than dictating treatment on its own. The result is interpreted along with your symptoms and, often, your urinalysis.

If you have symptoms and a meaningful amount of a single microorganism grew, your doctor uses the susceptibility results to choose an antibiotic likely to work. A doctor may start an antibiotic before the culture results are final, based on the most common causes, and then adjust it once the results are available. A repeat culture is usually not needed if your symptoms clear. If you have frequent or recurrent UTIs, your doctor may recommend further tests to identify an underlying cause.

Questions to ask your doctor

Did anything grow in my urine culture, and what was it?
Does my colony count point to a true infection, or could it be contamination?
Do my symptoms match the result of the culture?
If bacteria were found but I have no symptoms, do I need treatment?
Which antibiotics is the microorganism susceptible to?
Why was the antibiotic I am taking chosen, and is it one the report lists as susceptible?
Could a recent antibiotic have affected my result?
Do I need a repeat culture after treatment?
I get UTIs often. Should I have further tests to find out why?
Who should I contact if my symptoms get worse while I wait for the final result?