Urine tests can help find out if you have a urinary tract infection (UTI). Urinalysis and urine culture (MC/S) look for the bacteria that cause infection and sensitivity testing can show which antibiotics are likely to be effective in treating the infection. UTIs affect the bladder and/or the kidneys. Bladder infections are more common and are known as uncomplicated UTIs or cystitis. They occur when bacteria get into the urethra – the tube through which the urine leaves the body – and travel up into the bladder. A complicated UTI is when the infection travels beyond the bladder up to the kidneys.
Urine is one of the body’s waste products. It is produced in the kidneys and collected in the bladder until you urinate. Urine in the bladder is normally sterile - it contains no organisms. However, if bacteria or yeasts get into the urinary tract, they can multiply and cause a UTI.
Bacteria are found on the skin and around the opening of the urethra – the tube through which the urine leaves the body. Urine sample collection for culture (MCS) must be performed carefully in order to avoid contaminating the sample with these bacteria.
Because urine itself can serve as a culture medium, any bacteria present, including contaminating microorganisms, will multiply rapidly if the urine sample is allowed to stand at room temperature. For this reason, urine samples should be refrigerated (at about 4°C) after collection and transported to the laboratory as soon as possible.
UTIs in women and men
If you are a woman and have symptoms that are typical of bladder infection, your doctor may prescribe antibiotics without ordering tests. You’ll be offered an antibiotic which is known to work for most UTIs. By far the most common bacterium found in a UTI is E. coli and it can be treated by several different antibiotics. If your doctor thinks tests are needed, they will ask you to collect a urine sample.
UTIs in men are uncommon although they are more likely to occur with increasing age. Prostate infection, known as prostatitis, could be the reason for UTI-like symptoms in men. The doctor may order further tests to exclude prostate infection or underlying structural abnormalities or kidney stones. Sexually transmitted infections should always be considered as they can cause symptoms that mimic UTI.
Uncomplicated UTIs – also called cystitis
These mainly occur in women. Symptoms include a burning feeling when you pass urine, needing to urinate often, or finding blood in your urine. Sometimes urine can be cloudy and strong smelling. Most are caused by E. coli – Escherichia coli (about 75% - 95% of all cases) - and Staphylococcus saprophyticus (about 5% – 10% of all cases).
Complicated UTIs
A complicated UTI is when the infection travels beyond the bladder up to the kidneys. This is more serious. Kidney infections have similar symptoms to UTI - but also can cause fever, back pain, nausea and vomiting.
These mostly occur in people with underlying health problems. E. coli is the most common cause (20 to 50% of cases), but a wider range of bacteria such as Klebsiella, Proteus, Pseudomonas species also cause infection. Symptomatic UTIs caused by yeasts such as Candida are uncommon.
Pregnancy
It is recommended that pregnant women in the first trimester – the first three months of pregnancy – even without symptoms should be screened for bacteria in their urine as there is an increased risk of developing kidney infection (pyelonephritis) in later pregnancy.
Testing
A urine sample is not always required for culture in non-pregnant women with a first episode of uncomplicated UTI. Treatment can usually be started based on symptoms or with a dipstick test done in the clinic or doctor's surgery. The dipstick checks for leukocytes, nitrites and traces of blood, which are all signs of bacteria.
If you have an infection, your doctor may decide to send your urine sample to the lab for testing. Once in the lab, your urine sample will be checked under the microscope or a cell counting instrument to count the number of white blood cells (pus cells), red blood cells and skin cells. Large numbers of pus cells are strongly indicative of a UTI. Mixed bacterial types or large numbers of skin cells suggest that the sample hasn’t been collected properly and is contaminated, and you may need to provide another sample.
Next, the urine is streaked onto an agar plate and incubated at just the right temperature for any bacteria to grow. The culture is usually considered negative if no significant growth is found on the plates after 24 hours. Occasionally culture times may be lengthened to look for unusual organisms. Usually, if you have a UTI, the lab will see a lot of only one type of bacterium growing on the plate which is then identified and given a name – such as E. coli.
Organisms are identified by growth characteristics, proteomic testing with MALDI-ToF (mass spectrometry testing) and/or additional biochemical testing. The lab will then perform susceptibility testing to see which antibiotics will be effective for killing the bacteria. This involves adding different antibiotics to the cultured bacteria.
Sample
A ‘mid-stream’ urine is required to help avoid bacteria that lives on the skin, around the urethra, and on the hands getting into the sample.
Test preparation?
None
A negative culture usually means that there is no laboratory evidence of infection. However, a culture may be repeated if symptoms persist.
| RESULT | MEANING |
| Symptoms of a UTI plus pus cells and bacteria | There is an infection and prompt antibiotic treatment is recommended to prevent complications of infection. |
| No pus cells on urine testing | A UTI is unlikely and antibiotic treatment is usually not indicated. |
| No symptoms of a UTI but evidence of bacteria in the urine sample | This is termed asymptomatic bacteriuria and antibiotic treatment should be avoided. Asymptomatic bacteriuria becomes common with age. Treating with antibiotics where there are no symptoms is not beneficial, may cause side-effects and promote antibiotic resistant organisms. Treatment of asymptomatic bacteriuria is only required in pregnant women. |
| Large numbers of pus cells but no bacteria | This is called sterile pyuria. It can occur
In this situation, a sexually transmitted infection (STI) screen can be performed on the urine sample to check for organisms such as chlamydia and gonorrhoea |
The choice of tests your doctor makes will be based on your medical history and symptoms. It is important that you tell them everything you think might help.
You play a central role in making sure your test results are accurate. Do everything you can to make sure the information you provide is correct and follow instructions closely.
Talk to your doctor about any medications you are taking. Find out if you need to fast or stop any particular foods or supplements. These may affect your results. Ask:
Pathology and diagnostic imaging reports can be added to your My Health Record. You and your healthcare provider can now access your results whenever and wherever needed.
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