Urine Culture
Tests whether bacteria grow from your urine and, if they do, which kind and how many. It helps your clinician judge whether an infection is likely.
AI-drafted. Awaiting verificationAlso called UCxLOINC 630-4
What it is
A urine culture puts a small amount of your urine in a dish that helps bacteria grow. If bacteria grow, the lab counts them, reported as colony-forming units per milliliter (CFU/mL), and names the type. A second step, called susceptibility testing, shows which antibiotics are likely to work. First results usually take one to two days, sometimes longer.
Why it matters
A culture helps confirm a urinary tract infection (UTI) when you have symptoms, and shows which germ is involved so treatment can fit it. Bacteria can also be in the urine without any symptoms, called asymptomatic bacteriuria. Guidelines advise testing for and treating that only in a few situations, such as pregnancy or before certain urologic procedures. Antibiotics only treat bacterial infections, so a culture helps your clinician decide whether they are needed.
If it’s low
No growth means no bacteria grew from your sample. This makes a bacterial UTI less likely, but it does not explain every urinary symptom. Antibiotics taken before the sample, or symptoms from another cause, can also give no growth.
Common causes
- No bacterial infection of the urinary tract that grows on routine culture
- Antibiotics taken before the sample was collected
- Symptoms from another cause, such as irritation, inflammation or a different type of infection
What can help
- If you still have symptoms, tell your clinician so other causes can be checked
If it’s high
An organism was identified, usually because it grew at or above the lab's reporting threshold. For adults that is commonly about 100,000 CFU/mL, though a lower count can matter in some situations, such as in men, after partial treatment, or with coliform bacteria like E. coli. With UTI symptoms this can point to an infection. Without symptoms it can be asymptomatic bacteriuria. Your clinician reads it together with your symptoms and urinalysis.
Common causes
- A urinary tract infection (UTI), such as a bladder or kidney infection
- Bacteria in the urine without symptoms (asymptomatic bacteriuria)
- Contamination with skin or genital bacteria, especially if more than one type grew
- A urinary catheter in place, which often carries several types of bacteria
What can help
- Talk with your clinician about your symptoms and whether this result needs treatment
- Ask what the susceptibility results mean, since they show which antibiotics are likely to work
- If contamination is possible, ask how to give a clean-catch midstream sample for a repeat
What can affect your result
- How the sample was collected: midstream clean-catch, catheter or bag
- Antibiotics taken before the sample
- Time between collection and testing
- Contamination from skin or genital bacteria
- Age and sex: the count that counts as significant differs for adults, children and men
- Antibiotics taken before the sample can stop bacteria from growing and give a falsely negative or low-count result.
- Skin or genital bacteria getting into the sample can cause mixed growth or a false-positive result. A midstream sample with genital cleansing is recommended.
- Urine left at room temperature for hours before testing can give unreliable counts. Refrigerate it or test it promptly.
- A sample from a bag stuck to a baby's skin, or from a catheter bag, is more likely to be contaminated.
Any time. Give a midstream clean-catch sample, and get it to the lab or into the refrigerator promptly. Reflects the bacteria in the urine when you gave the sample. The lab usually needs one to two days to grow them, and longer for slow-growing bacteria.
When to talk to a clinician
Contact a clinician soon if you have burning when you urinate, needing to go often, or pain low in your belly. Seek urgent care for fever with back or side pain, shaking chills, vomiting or confusion, especially in older adults. If you are pregnant, tell your clinician about any positive urine culture, even if you feel fine.
Questions you could ask
- Was my sample collected the right way?
- Do I need a repeat culture later, for example in pregnancy or after treatment?
- Does this result need treatment, given my symptoms?
- Could this be contamination, and should we repeat with a clean-catch sample?
- What do the susceptibility results mean for my options?
- If my symptoms continue even though nothing grew, what else should we check?
Questions people ask
What does 100,000 CFU/mL mean?
CFU/mL stands for colony-forming units per milliliter, a count of how many bacteria were in each milliliter of urine. For adults, about 100,000 CFU/mL or more of one organism is the usual cutoff for a urinary tract infection, but lower counts can matter in some cases. Your symptoms matter as much as the number.
My culture says mixed flora. Do I have an infection?
Mixed flora means several types of bacteria grew with no clear main one. That often happens when a sample picks up germs from the skin or genital area, so it is often not a clear sign of infection. If you have symptoms, your clinician may ask for a new clean-catch sample.
How long do urine culture results take?
Usually one to two days for the first result. Slow-growing bacteria and susceptibility testing can take longer.
Show the science and sources
For clinicians and researchers
Quantitative culture of a voided midstream or catheter specimen reports organism(s) and colony count (CFU/mL), with susceptibility testing for significant isolates. Thresholds depend on the setting. AFP 2022 lists a minimum of 100,000 CFU/mL for adults and 50,000 for infants and children (10,000 at physician discretion), and suggests considering 100 to 1,000 CFU/mL for male genitalia, partially treated UTI or coliform bacteria. IDSA 2019 defines asymptomatic bacteriuria as 10^5 CFU/mL or more in a voided specimen without symptoms, confirmed by two consecutive specimens in women and a single specimen in men; in catheterized patients, 10^2 to under 10^5 CFU/mL from an in-and-out or new indwelling catheter may suggest true bacteriuria. EAU uses the same 10^5 CFU/mL threshold for asymptomatic bacteriuria in a midstream sample, confirmed in two consecutive samples in women and in one sample in men. A dominant organism is what a culture is used to find (AFP 2022), and growth of several types is commonly reported as mixed flora, with reporting rules that vary by lab. The American Society for Microbiology recommends midstream collection with genital cleansing, although evidence that this lowers contamination is limited (cited in AFP 2022). Bag collection overstates bacteriuria because of contamination (IDSA 2019). Screening for asymptomatic bacteriuria is recommended in pregnancy and before endoscopic urologic procedures with mucosal trauma (IDSA 2019, AFP 2022).
LOINC 630-4 (primary), 100906-7. Specimen: urine.
Sources
- Office-Based Urinalysis: A Comprehensive Review, American Family Physician 2022;106(1):27-35B (2022)
- IDSA 2019 Clinical Practice Guideline Update for the Management of Asymptomatic Bacteriuria, Infectious Diseases Society of America (Clinical Infectious Diseases 2019;68(10):e83-e110) (2019)
- EAU Guidelines on Urological Infections, European Association of Urology
- Bacteria Culture Test, MedlinePlus (U.S. National Library of Medicine)
- LOINC codes verified with the NLM Clinical Tables LOINC search, U.S. National Library of Medicine
AI-drafted. Awaiting verification. Last reviewed 2026-10-03. How we build and check these pages.