- What Is Urine Culture?
- How Is Urine Culture Done?
- Urine Culture Report
- “No Growth” on Urine Culture
- Urine Culture FAQs
What is Urine Culture?
- Urine culture is a method to find the cause of urinary tract infections (UTIs). Normally, urine does not contain any microbes, but in people with a UTI it is full of the one causing the infection. A urine culture can show the microbe present, and most importantly, identify it very precisely.
- It is often followed by a test to find out the antibiotic that will work best against the microbe found. These two tests are together called as urine culture and sensitivity (UCS).
How is Urine Culture Done?
- A quick look at how urine culture is done will help you understand your report better. In laboratory language urine culture means to “grow" microbes present in urine by putting a small amount of it in a special gel (media) containing all the nutrients needed by the microbes.
- The media used in a standard urine culture can support the growth of all the common bacteria causing UTIs. If any of them is present, it multiplies rapidly and forms tiny clumps called colonies.
- Each type of bacteria forms colonies of unique size, shape, and color. A trained lab person can tell just by looking which microbe it belongs to, or do more tests to identify it. The labs also have methods to estimate the number of microbes/mL of urine from the number of colonies formed.
Urine Culture ReportThe culture report mentions the type of bacteria found and states the number of colony forming units (CFU)/mL of urine.
- If you have a UTI, loads of any one type of bacteria are expected to grow on culture, typically more than 100,000 colony forming units (CFU)/mL are seen. However, even 1000 CFU/mL of one type of bacteria may mean an infection is present if you have symptoms.
- Lower numbers usually indicate sample contamination, which is quite frequent because the common bacteria causing UTIs are also normally found in your anal and genital area and can get into the urine sample while you are collecting it.
- Growth of more than one type of bacteria in significant number may occur because of contamination. A repeat test may be needed.
- Anything more than 1000 CFU/ mL from a sample collected through a catheter indicates infection since sample contamination is unlikely.
“No Growth” on Urine Culture
- You have all the symptoms of a UTI, your urine shows pus cells, but nothing grows on culture. This is a tricky situation that requires a careful history, right investigations, and definitely a good doctor.
- Most simply, no growth could mean there are no microbes and something other than infection is responsible for your symptoms. Some possibilities are stones, interstitial cystitis and prostate involvement in men. A urologist is usually the right doctor to handle such cases.
- A lab may say “no growth” or “no significant growth” when the number of bacteria is less than a predefined cut-off level because they assume it to be because of sample contamination. For this reason, many doctors prefer to treat their patients for common UTIs, if symptoms and pus cells are present, even if there is no growth reported on culture.
- The media used in standard urine culture is suitable only for the common bacteria causing UTIs. “No growth” will occur if your symptoms are caused by an uncommon organism that requires special media to grow. Some microbes are very finicky, and won’t easily grow on any media that you use. Your doctor may order special culture or tests to detect less common organisms such as Neisseria, Chlamydia, Ureaplasma, Mycoplasma, Trichomonas, and Mycobacteria.
- No growth may happen if you have recently taken antibiotics for any reason.
Urine Culture FAQs
- Why Is It Not Done In All UTI Cases?
Don’t be bothered if your doctor didn’t suggest a urine culture before treating your UTI. A dipstick test or microscopic examination of urine can reliably diagnose a UTI. They do not tell the bacteria causing it, but since most cases are caused by a small group of related bacteria that respond to the same type of antibiotics, a precise identification is not necessary for treatment. Moreover a culture report can take up to 2 days during which your symptoms may worsen. However, with the growing increase in the number of bacteria that do not respond to common antibiotics, urine culture and sensitivity may be a good decision in many cases.
- When Is It Necessary?
Urine culture and sensitivity is necessary if:
- The infection doesn’t go or recurs shortly after treatment.
- A kidney infection is suspected.
- You are a male. Since UTIs are relatively uncommon in men, underlying complications that predispose to infection are suspected.
- Can Urine Culture Find All Causes of UTIs?
- As we said above, a standard urine culture is suitable only to find the common bacteria causing UTIs, which is quite sufficient in majority of the cases. But your symptoms may be caused by an uncommon organism that requires special culture techniques or other tests. UTI-like symptoms may also be caused by conditions other than infection.
- Your doctor can order more tests based on your risk factors, symptoms and history if a urine culture fails to establish the cause of your symptoms.
- How to Collect a Good Sample for Culture?
Your doctor or lab may instruct you to give a mid-stream clean catch sample. Here’s how you go about doing that:
- Avoid passing urine for at least an hour before collection so that you can produce enough urine to give a sample.
- Wash your hands before collecting the urine. If you are a male, retract the foreskin, and wipe the head of penis with a swab. Women should spread the labia (skin folds around vagina) and wipe the area from front to back so that bacteria around anus are not drawn towards the urethra.
- Women should use a tampon if giving the sample during periods.
- Let some urine pass into the toilet. Then place the container in the stream and collect the “midstream” urine. Try not to touch the rim of the container to your skin.
- Finish urinating into the toilet. Close the container and wash your hands. Samples collected at home should be stored in a fridge and given to the lab within a day.