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Common Laboratory Tests
Most UTIs are detected by performing a urinalysis and then confirmed with a urine culture. If there are (disease-causing) bacteria present, then susceptibility testing is done to make sure that the antibiotic that the doctor chooses will effectively treat the causing the infection.
Urinalysis. A clean catch (midstream) sample collection is important to minimize sample contamination with skin cells and non-pathogenic bacteria that might be just residing on the skin. White blood cells (WBC, leukocytes), red blood cells (RBC), nitrites, and bacteria in the urinalysis may indicate a UTI.
Urine Culture. Urine is streaked on a thin layer of nutrient gel (agar plate), then incubated for 24-48 hours.
If bacteria are present they will grow as colonies on the agar plate. Usually, if a person has a UTI, there will be a high colony count of one type of present which will then be identified (eg. given a name such as E.coli) and susceptibility testing done (often referred to as “sensitivity” testing) to determine which antibiotics will be effective. If there are more than two types of bacteria present the sample is considered to be contaminated, usually due to an inappropriate collection method (i.e. not a midstream sample) and no further work is done on the culture. A repeat sample may need to be submitted if symptoms persist.
Follow-up Laboratory Tests
If a doctor suspects that a UTI may have spread into the bloodstream, a blood culture may be ordered. If symptoms are suspected to be due to a sexually transmitted infection (STI), such as chlamydia or gonorrhoea, then specific tests for STIs will be ordered on the urine sample.
In the case of recurrent or urinary tract infections, other laboratory tests such as glucose (to check for diabetes) or urea and creatinine (to evaluate kidney function) may also be done.
Blood Culture. Two samples of blood are taken to look for the presence of bacteria in the blood, which is normally sterile (no bacteria present). The blood samples are incubated in a broth culture medium at body temperature and monitored for bacterial growth. Most urinary organisms causing bloodstream infections will be detected within 24-48 hours, with the same organism being found in both urine and blood.
Susceptibility testing will provide information on which antibiotic will eradicate the from both the blood and the urine.
Imaging scans and special X-rays may also be used to look structural or functional problems and/or signs of an underlying disease or condition. If a person has recurrent or chronic UTIs, one or more of the following procedures may be ordered. Each gives the doctor different information.
Kidney and bladder ultrasound - uses sound waves to determine the structures of the bladder and the kidney.
Voiding cystourethrogram (VCUG) - an x-ray test that examines the urethra and bladder while the bladder fills and empties
Kidney and bladder CT scans- a scan (commonly known as a CAT scan) that uses multiple beams of x-rays to give detailed views of the structures of the urinary tract to look for evidence of kidney infection or abscess along with any blockages in the urinary tract.
Nuclear scans - several types may be used to examine the function and shape of the bladder and kidneys. For each scan type, a radioactive dye is injected into a vein. The dye is carried to the bladder and kidney, allowing the visualization of any structural abnormalities.
Cystoscopy - a flexible tube about the diameter of a straw is threaded up the urethra and into the bladder. It allows a doctor to look at the surface of the inside of urethra and bladder. It can help identify blockages and abnormalities. If a stone is present, other instruments can be inserted up through the cystoscope that may allow a stone to be removed or broken into smaller pieces with a laser. The crushing of these stones is called lithotripsy. Urine and tissue sample can also be taken using the cystoscope.
Intravenous pyelogram (IVP) - used to look at the whole urinary tract. An opaque dye is injected into a vein, then travels to the kidney and bladder. A series of x-rays are taken, which may reveal obstructions or structural abnormalities.
Last Review Date: November 13, 2019