How do physicians diagnose a urinary tract infection?
Diagnosis of a urinary tract infection is based on information someone gives about his or her symptoms, medical and surgical history, medications, habits, and lifestyle. A physical examination and lab tests complete the evaluation.
A doctor may simply perform a urine dipstick test in the office. Only a few minutes are needed to obtain results. A doctor may also send a urine sample to the lab for culture testing (see below). These results take a few days to come back. This tells the doctor the exact bacteria causing the infection and to which antibiotics these bacteria have resistance or sensitivity. The culture is usually sent for special populations, including men, because they are less likely to get UTIs. It is not necessary to send a culture for everyone because the majority of UTIs are caused by the same bacteria.
- The single most important lab test is urinalysis. A urine sample will be tested for signs of infection, such as the presence of white blood cells and bacteria.
- In certain circumstances, urine also may be "cultured." This means that a small amount of the urine is brushed on a sterile nutrient substance in a plastic plate. The plate is allowed to sit for a few days and then examined to see what kind of bacteria are growing on it. These bacteria are treated with different antibiotics to see which works best against them. This helps determine the best treatment for the specific infection.
- Blood tests usually are not required unless a complicated condition, such as pyelonephritis or kidney failure, is suspected.
For a culture specimen, the patient will be asked to give a clean-catch, midstream urine specimen. This avoids contamination of the urine with bacteria from the skin. Patients will be instructed in how to do this.
- Midstream means urinating a little into the toilet before collecting a specimen. The idea is to avoid collecting the urine that comes out first, as this urine is often contaminated.
- Clean-catch refers to a midstream sample that was collected after cleaning the area of the urethral opening.
- Adult women and older girls: Cleanse the area around the urethral opening gently (but completely) using a sterile wipe or soap and water. Catch the urine midstream. For some women, catheterization (inserting a tube into the bladder) may be the only way to obtain a sterile, uncontaminated specimen.
- Men and boys: A sterile specimen can usually be obtained with a midstream catch. Uncircumcised males should retract the foreskin and cleanse the area before urinating.
- Newborns: Urine may be obtained with a catheter or a procedure in which a needle is introduced through the lower abdominal wall to draw (aspirate) urine from the bladder.
- Infants and children: Either catheterization or the needle aspiration method is used.
If someone cannot produce a urine specimen or is unable to follow instructions for a clean-catch specimen, a health-care professional may obtain a urine specimen by catheterization.
- This means placing a thin tube (catheter) in the urethra to drain urine from the bladder.
- The catheter usually is removed after the bladder is emptied.
- The catheter may remain in place if someone is very ill or if it is necessary to collect all urine or measure urine output.
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- An ultrasound examination can evaluate kidney and bladder problems.
- A fluoroscopic study can show any physical problems that predispose children to urinary tract infections.
- Intravenous pyelogram (IVP) is a special series of X-rays that uses a contrast dye to highlight abnormalities in the urinary tract.
- Cystoscopy involves insertion of a thin, flexible tube with a tiny camera on the end through the urethra into the bladder. This allows detection of abnormalities inside the bladder that might contribute to infections.
- A CT scan gives a very detailed three-dimensional picture of the urinary tract.
Imaging tests are most often needed for the following groups:
- Children with urinary tract infections, especially boys
- Up to 50% of infants and 30% of older children with a urinary tract infection have an anatomic abnormality. The child's pediatrician should investigate this possibility.
- Adults with frequent or recurrent urinary tract infections
- People who have blood in the urine