Urinary Tract Infection (UTI)

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Most UTIs are detected by performing a urinalysis.  Treatment may be started at this stage.  If symptoms persist, UTI may be confirmed with a urine culture. If there are pathogenic bacteria present, then antibiotic susceptibility testing is done. This is to make sure that the antibiotic that your doctor chooses will have good activity against the bacteria causing your infection. If your doctor suspects that your infection may have spread to your bloodstream, they may refer you to hospital where they will take a blood sample for culture. If your doctor suspects that you may have a sexually transmitted disease, such as chlamydia or gonorrhoea – which may cause some of the same symptoms as a bacterial UTI – they may do additional  testing to identify them.

In the case of recurrent or chronic urinary tract infections, other laboratory tests such as glucose (to check for diabetes), or urea and electrolytes (U&E) and creatinine (to evaluate your kidney function) may also be done. Imaging scans and special X-rays may also be used to look for anatomical problems and/or signs of an underlying disease or condition.

Laboratory Tests
Urinalysis. A clean (midstream) sample collection is important to minimise sample contamination by skin cells and bacteria (and, in the case of women, contamination by normal vaginal bacteria). The patient should clean their urogenital area thoroughly with soap (not anti-bacterial) and water before providing a urine specimen. 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. Any bacteria that grow on the agar are counted and identified. Usually if a person has a UTI, there will be a high colony count of one type of bacterium that will be present. If there are three or more types of bacteria present (or in a woman if there are vaginal bacteria, such as lactobacillus or diphtheroids) then it is considered to be a contaminated sample and no further work is done on the culture. A repeat sample may need to be submitted if the patient's symptoms persist. If there is a predominant growth of one type of bacterium present in high numbers, then antibiotic susceptibility testing is done (sometimes the doctor may refer to this as “sensitivity” testing). The ability of different antibiotics to inhibit the growth of the bacteria predicts which antibiotics will work best in the patient.

Blood Culture. Two samples of blood are taken to look for any bacteria in the blood, which is normally sterile. The blood samples are incubated in a broth medium at body temperature and examined at regular intervals for bacterial growth. Although most infections will be detected within 24 to 48 hours, if the number of bacteria is low or the bacterium is slow growing, it could take longer. Blood cultures are kept and monitored for five days. When a patient is septic from a urinary tract infection, the same microorganism is found in both the blood and the urine cultures. Antibiotic susceptibility testing will provide information on which antibiotic will eradicate the pathogen from both the blood and the urine.

Non-Laboratory Tests
If you have recurrent or chronic UTIs, your doctor may request one or more of the following procedures. Several may be required as they each give your doctor different information.

Kidney and bladder ultrasound, uses sound waves to determine the structures of the bladder and the kidney, they can be seen as light and shadowed areas.

Voiding cystourethrogram (VCUG), an x-ray test that examines the urethra and bladder while the bladder fills and empties

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 your 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. 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

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