The tests used to check for a UTI are urinalysis and urine culture. A urinalysis is a preliminary test that indicates whether there is any likelihood of a UTI. It can be done in a laboratory or using a simple dipstick method in a doctor’s office. It takes only a few minutes and can suggest the presence of an infection. A piece of paper (or dipstick) is dipped into the urine and then removed.
After two to three minutes, the paper changes color to signify what components have been found in the urine. A positive urinalysis, suggesting that there is an infection in the urine, shows that there are leukocytes or nitrites in the sample.
If the test is positive (or if it is negative but your child’s symptoms really seem to indicate a UTI), a urine culture will be done. A small amount of urine is transferred onto a special plate and left in an incubator for 24 to 48 hours. If bacteria grow on the plate, your doctor will identify the bacteria and prescribe an antibiotic that is effective.
Most potty-trained toddlers can produce a urine sample when asked, but toddlers in diapers generally need help with urine collection.
A urinalysis and a urine culture can be collected at the same time, as long as a sterile cup is used during the collection. A non-sterile cup can contaminate the urine culture, leading to false-positive results.
After the first (or certainly the second) UTI, it is standard to take a picture of the urinary tract to make sure there is no anatomical reason for the infection. Three tests can be used. An ultrasound illustrates the size and structure of the bladder, ureters, and kidneys. Ultrasound is entirely noninvasive but is not as definitive as the other two tests. A voiding cystourethrogram (VCUG) uses a special dye to light up the bladder, the ureters, and sometimes the kidneys. The dye is injected directly into the bladder using a tube inserted into the urethra. An X-ray device (called a fluoroscope) takes pictures to see whether the dye stays in the bladder or refluxes back up into the ureters and even the kidneys. An alternative detailed imaging study is a Tc-dimercaptosuccinic acid scan (DMSA scan). For this scan, a chemical is injected into a vein and is filtered out of the bloodstream through the kidneys. As the material flows through the urinary system, it outlines the urinary tract, identifying any abnormalities.
An ultrasound can be done during a UTI, but a VCUG or DMSA scan should be done only after the UTI is resolved. This is because a lingering infection can cause reflux of the urine, resulting in false-positive results. These results suggest abnormal anatomy of the urinary tract when in fact the urinary tract is structurally normal. Once a UTI is completely gone, a VCUG or DMSA scan will accurately represent the structure of the kidneys, ureters, bladder, and urethra.