Urine culture

No special preparation is usually needed. However, you may be asked not to urinate for at least one hour before collecting the sample, or to drink a glass of water 15–20 minutes beforehand, to make sure you can produce enough urine. 

How you collect the sample is important. Bacteria from the skin around the urethra can easily contaminate the sample and give a misleading result. Follow the midstream clean-catch method: 

• wash your hands thoroughly before starting 
• women: hold the labia apart while urinating, to reduce contact with surrounding skin 
• men: clean the tip of the penis before collecting 
• start to urinate into the toilet — do not collect this first part of the stream 
• without stopping, move the sterile container into the flow to collect a mid-stream sample, then finish into the toilet 
• seal the container tightly and label it with your name and date of birth 
• take the sample to the laboratory or GP surgery as soon as possible — ideally within one to two hours 
• if you cannot deliver it straight away, store the container in the fridge — but no longer than 24 hours 

What the test measures 

Healthy urine does not contain significant numbers of bacteria or other microorganisms. A urine culture finds out whether bacteria or yeast are present in your urine, identifies what type they are, and tests which antibiotics will kill them. 

The culture is usually part of a broader test called MC&S — microscopy, culture and sensitivity. First, the laboratory examines the sample under a microscope (microscopy) to look for white blood cells, bacteria, and other signs of infection. If the microscopy suggests infection, the sample is cultured: it is spread on a nutrient plate and left to incubate overnight at body temperature, to allow any bacteria or yeast to grow into visible colonies. The colonies are then counted and identified. 

Finally, sensitivity testing — also called susceptibility testing — checks which antibiotics are effective against the bacteria found. This helps your doctor prescribe the right antibiotic and supports the NHS approach of using narrow-spectrum antibiotics wherever possible, to reduce antibiotic resistance.

What your results mean 

Negative result — no significant growth 

A negative result means the culture found no significant bacteria or yeast in your urine. This usually means you do not have a UTI. 

However, a negative culture does not always mean the urine was completely free of microorganisms. If your symptoms persist, your doctor may repeat the test or consider other possible causes for your symptoms — such as a sexually transmitted infection, bladder irritation, or urethral inflammation. Always follow up with your doctor if you are still unwell after a negative result. 

Positive result — bacteria or yeast identified 

A positive result means bacteria or yeast were grown from your urine. The report will usually state: 

• the name of the organism found — for example, Escherichia coli (E. coli), the most common cause of UTIs, which normally lives in the bowel; other common bacteria include Klebsiella, Proteus, and Staphylococcus saprophyticus 
• a colony count — reported as the number of bacteria per millilitre of urine (for example, >100,000 CFU/​mL); higher counts generally indicate true infection rather than contamination, though lower counts can still be significant in some patients 
• a sensitivity panel — a list of antibiotics tested against the bacteria, with each marked as sensitive (S), intermediate (I), or resistant ®; your doctor will use this to prescribe or confirm the most effective treatment 

If yeast such as Candida are found, this often represents colonisation rather than a true urinary tract infection, particularly in people with urinary catheters. Your doctor will interpret the result alongside your symptoms and other clinical findings. 

Mixed growth or contaminated sample 

If several different types of bacteria are found in low quantities, the result may be reported as ​“mixed growth” or ​“possible contamination.” This usually means the sample was contaminated during collection — by skin bacteria from around the urethra — rather than showing a true infection. 

In this case, your GP surgery may ask you to provide a fresh sample. This is very common and does not mean anything is seriously wrong. Collecting the sample carefully using the midstream clean-catch method (described above) reduces the chance of this happening. 

Antibiotic-resistant bacteria 

Occasionally, the culture may find bacteria that are resistant to commonly used antibiotics. Your doctor will review the sensitivity panel and prescribe an antibiotic that the bacteria are still susceptible to. If you are already taking an antibiotic that the report shows to be ineffective, your doctor will contact you to switch your treatment. It is important to complete any prescribed course of antibiotics even if you feel better. 

UTI in men — further investigation 

UTIs are much less common in men than in women. A confirmed UTI in a man — particularly in a young or middle-aged man — may prompt your doctor to investigate further, for example with an ultrasound scan, to look for an underlying cause such as a kidney stone, an enlarged prostate, or a structural abnormality of the urinary tract.

For most people with a straightforward UTI, a urine culture confirms the infection and guides antibiotic treatment. Most lower UTIs (affecting the bladder) resolve quickly with a short course of antibiotics — usually three to seven days. 

If you were prescribed antibiotics before the culture result was available, your doctor will review the sensitivity panel once the result is back. If the antibiotic is effective, you continue the course. If the bacteria are resistant, your doctor will work with you to switch to the right treatment. 

If you have a kidney infection (pyelonephritis), treatment is usually longer — typically 7–14 days — and you may need hospital admission if you are very unwell. A repeat culture after treatment may be requested to confirm the infection has cleared, particularly in pregnancy. 

For recurrent UTIs, your doctor may investigate further or refer you to a specialist. For more information on UTIs, visit NHS: Urinary tract infections (UTIs).

• Contamination during collection: the most common cause of misleading results; collecting the first part of the urine stream, not cleaning the genitalia beforehand, or touching the inside of the container can all introduce skin bacteria into the sample — careful midstream clean-catch collection prevents this 
• Antibiotics taken before sample collection: even a single dose of antibiotics can suppress bacterial growth and cause a false negative result; if possible, collect the sample before starting antibiotics, or tell the laboratory that antibiotics have been taken 
• Delay between collection and testing: bacteria multiply rapidly at room temperature — samples left too long before reaching the laboratory may show falsely high colony counts; refrigerate if there will be a delay, but aim to deliver within two hours 
• Dehydration: very concentrated urine can inhibit bacterial growth and may produce a false negative; drinking a small amount of water before collection can help 
• Menstruation: blood in the sample can interfere with microscopy and culture; tell your doctor or nurse if you are menstruating, and if possible wait until your period has ended before collecting a sample for culture 
• Catheter specimens: urine collected from a long-term urinary catheter may grow bacteria that have colonised the catheter without causing active infection (catheter-associated bacteriuria); interpretation requires clinical judgement and should not automatically lead to antibiotic treatment 

• Urinalysis — dipstick test often performed first; if abnormal, a culture is sent to the laboratory 
• Susceptibility testing — the antibiotic sensitivity panel that forms part of the MC&S result 
• U&E (urea and electrolytes) — blood tests to check kidney function if a kidney infection is suspected 
• eGFR — estimated kidney filtration rate, assessed alongside U&E in kidney infection 
• Urine albumin to creatinine ratio (ACR) — to check for kidney damage in people with recurrent UTIs or kidney infection 

UTIs are among the most common bacterial infections in the UK. They are caused by bacteria — most often E. coli from the bowel — entering the urethra and moving up into the bladder. Women are affected more often than men. Most UTIs are easily treated with antibiotics. For more information, visit NHS: Urinary tract infections (UTIs).