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Urinary Tract Infection


An in-depth report on the causes, diagnosis, treatment, and prevention of urinary infections.


Often UTI symptoms in young women plus positive results on an over-the-counter dipstick test are enough to make a diagnosis. They include frequent urination and, in women, vaginal burning, without other complications, such as fever, chills, and pain in the kidney. In such cases, young women can now often receive treatment with a simple phone call to a health professional (usually a nurse) who will prescribe antibiotics. A good response to antibiotic therapy usually eliminates the need for further tests.

This course is now recommended only for nonpregnant women at low risk for recurrent infection and who do not have symptoms suggesting other problems, such as vaginitis. In some centers, women who are treated over the phone have to be less than 55 years old; other patients need to see a physician for evaluation. Pregnant women should be screened for E. coli because of the risk of complications, including miscarriage, from certain strains of this bacteria.

Ruling Out Other Conditions with Similar Symptoms

About half of women with symptoms of a UTI actually have some other condition, such as irritation of the urethra, vaginitis, interstitial cystitis, or sexually transmitted diseases (STDs). Some of these problems may also accompany or lead to UTIs.

Vaginitis. Vaginitis is a common vaginal infection that can be caused by a fungus (candidiasis) or bacteria. Occasionally, the infection causes frequent urination, mimicking cystitis. The typical symptoms of vaginitis are itching and an abnormal discharge.

Sexually Transmitted Diseases. Women with painful urination but whose urine does not exhibit signs of bacterial growth in culture may have a sexually transmitted disease. The most common culprit is the organism Chlamydia trachomatis. Other STDs that may be responsible include gonorrhea and genital herpes.

Interstitial Cystitis. Interstitial cystitis (IC) is an inflammation of the bladder wall that occurs almost predominantly in women. The average age of patients with IC is 40, but 25% of cases occur in women under 30. Symptoms are very similar to cystitis, but no bacteria are present. Pain during sex is a very common complaint in these patients, and stress may intensify symptoms.

Bladder Cancer. Bladder cancer is a rare cause of painful urination and is more common in men than in women.

Kidney Stones. The pain of kidney stones along with blood in the urine can resemble the symptoms of pyelonephritis. There are no bacteria present with kidney stones, however.

Thinning Urethral and Vaginal Walls. After menopause, the vaginal and urethral walls become dry and fragile causing pain and irritation that can mimic a UTI.

Disorders in Children that Mimic UTIs. Problems that might cause painful urination in children include reactions to chemicals in bubble bath, diaper rashes, and infection from the pinworm parasite.

Prostate Conditions in Men. Prostate conditions, including prostatitis (inflammation of the prostate) and benign prostatic hyperplasia, can cause symptoms similar to urinary tract infections.

BPH Click the icon to see an image of benign prostatic hypertrophy.

Physical Examination

During an exam, the physician should examine the pelvic and vaginal area in women. Men require a digital rectal examination to determine if prostate enlargement is present. The physician will also examine the male genitals for signs of infection. In both men and women, the physician should also check the abdomen and areas around the kidneys for swelling and tenderness.

Digital rectal exam
With the exception of skin cancer, prostate cancer is the most common type of cancer among men in the United States. Early detection may result from a blood test called a PSA (prostate-specific antigen), and/or a digital rectal exam. The digital rectal exam checks the rear surface of the prostate gland for any abnormalities. A lump or hardness found during the exam might be a sign of prostate cancer.

Dipstick Tests

Dipstick tests, available over the counter, are quite reliable in making a reasonable diagnosis of UTIs in women with symptoms. Dipstick tests may also be useful for identifying UTIs in children and infants. The test employs a chemical on a stick dipped in urine that reacts to nitrites, substances produced by many of the bacteria that cause UTIs. A positive test (which indicates that an infection is present) can now often supplant urine cultures, a more expensive test used for detecting bacteria. A negative dipstick test helps to avoid unnecessary antibiotics, which are contributing to the growing problem of antibiotic resistance. They are not entirely accurate, however, and studies report that they may miss up to 25% of actual UTIs. If a woman has persistent UTI symptoms and the dipstick test is negative, she should check with her physician to see if more accurate tests are needed.

Urine Samples

A urine sample is needed for most extensive testing. In most cases, the physician requests a clean-catch sample. There are also other methods for collecting urine depending on the patient's condition.

Clean-Catch Sample. A clean-catch sample for UTI depends on a sample free of contaminants normally present at the opening of the urethra (e.g., white blood cells and bacteria unrelated to UTIs). To obtain an untainted urine sample, physicians usually request a so-called midstream, or clean-catch, urine sample. To provide this, the following steps are taken:

  • Patients must first wash their hands thoroughly, then wash the penis or vulva and surrounding area four times, with front-to-back strokes, using a new soapy sponge each time.
  • The patient must then begin urinating into the toilet and stop after a few drops.
  • The patient then positions the container to catch the middle portion of the stream. Ideally, this urine will contain only the bacteria and other evidence of the urinary tract infection.
  • The patient then urinates the remainder into the toilet.
  • The patient securely screws the container cap in place without touching the inside of the rim.

The sample is generally given to the physician or sent to the laboratory for analysis. For the majority of cases of suspected cystitis, this sample is considered adequate. In fact, a 2000 study reported that the clean-catch sample had identical contamination rates as a simple urine sample taken with no precautions. Researchers in the study suggested that in young, sexually active women with symptoms of cystitis, a urine sample may not even be necessary.

Incontinence Pads. Testing and diagnosing UTIs in elderly patients who are incontinent is especially difficult, because of the similarities in symptoms. Researchers have found that pressing a dipstick into an incontinence pad is an effective way to screen for urinary tract infections in incontinent patients.

Collection with a Catheter. Some patients (e.g., small children, elderly people, or hospitalized patients) cannot provide a urine sample. In such cases, a catheter may be inserted into the bladder to collect urine. This is the best method for providing a contaminant-free sample.


A urinalysis involves a physical and chemical examination of urine. In addition, the urine is spun in a centrifuge to allow sediments containing blood cells, bacteria, and other particles to collect. This sediment is then examined under a microscope. A urinalysis, then, offers a number of valuable clues for an accurate diagnosis:

  • Simply observing the urine for color and cloudiness can be important.
  • Acidity is measured.
  • White blood cells (leukocytes) are counted. A high count in the urine is referred to as pyuria. (A leukocyte count over 10 per microliter is considered to indicate pyuria.) This is very accurate in identifying the disease when it's present, but it also tests positive in many people who do not have a UTI. Pyuria is usually sufficient for a diagnosis of UTI in nonhospitalized patients if other standard symptoms (or just fever in small children) are also present.

Treatment can be started without the need for further tests if the following urinalysis results are present in patients with symptoms and signs of UTIs:

  • A high white cell count.
  • Cloudy urine.

Urine Culture

A urine culture uses a urine specimen that is placed on an agar plate, then incubated in the laboratory for 24 to 48 hours. It is then examined for the presence of bacterial growth. Urinary tract infection is nearly always caused by a single species of bacteria, notably E. coli. Cultures have limitations, however. If a mix of different species is found, the test is considered contaminated and is redone. In addition, even if E. coli is identified, researchers are also looking for variants of this bacteria. Certain types may indicate a higher risk for a second infection, while others may even be protective against recurring infections. Furthermore, some organisms, such as Chlamydia, which is a sexually transmitted organism, may not be detected.

A urine culture is usually performed if the dipstick results are positive, but even if the results are negative, a culture may still be helpful under certain circumstances:

  • If urinalysis or dipstick is negative but the patient has UTI symptoms, particularly if the patient has recurring infections or is in a high-risk group.
  • If the physician suspects complications.
  • In girls less than two years of age with a high fever of unknown origin that lasts two days or more.

Even if bacteria are present in the culture, a diagnosis of UTI depends on symptoms and gender:

  • The presence in a culture of at least 100,000 bacteria milliliter of any single type of bacterium per milliliter of urine usually provides conclusive evidence of infection in women with symptoms.
  • A count of 100,000 bacterial per milliliter in a woman without symptoms indicates asymptomatic bacteriuria. The decision to treat depends on the woman's risk factors for complications.
  • In young women with symptoms of cystitis, a diagnosis of infection can reasonably be made with counts as low as 1000 bacteria per milliliter.
  • Men are considered to have an infection with a count of only 1,000.

Gram Stain

If physicians suspect that bacteria other than E. coli may be present, a Gram stain is used to help predict the species. This is a staining procedure used to make bacteria visible through a microscope. Many bacteria are categorized by the terms gram-positive and gram-negative.

  • Bacteria that turn pink from staining are called gram-negative.
  • Those that turn blue are called gram-positive.

Escherichia coli is gram negative and the most common cause of UTIs. If physicians suspect that bacteria other than E. coli are causing a UTI, a Gram stain is useful for identifying other species.

Imaging Techniques

Because of the expense and the limited accuracy of imaging procedures, these techniques are used only for the following:

  • Serious and recurrent cases of pyelonephritis.
  • When structural abnormalities are suspected.
  • If infections do not respond to treatment.
  • If a physician suspects obstruction or an abscess.
  • After a first urinary tract infection in children two to 24 months to detect possible obstruction or vesicoureteral reflux. Tests include ultrasound and a voiding cystourethrogram and possibly scans. Some evidence suggests that ultrasound is probably not necessary, but at this time it is recommended by major medical groups.

Ultrasound. Ultrasound is a noninvasive, risk-free imaging test that can be used to screen for hydronephrosis (obstructions of the flow of urine), kidney stones that predispose to infection, and kidney abscesses. In men, ultrasound can detect enlargement or abscesses of the prostate and, when combined with x-rays, is an accurate method for detecting incomplete emptying of the bladder, a common cause of UTI in men over 50. In children with urinary tract infections, they also can be used to detect vesicoureteral reflux, the defect of the valve-like mechanism between the ureter and bladder. They are not as accurate as voiding cystourethrograms.

Nuclear Scans. Imaging techniques called nuclear scans may be useful in certain complicated cases, such as detecting kidney scarring after pyelonephritis in children. They produce better images and expose the patient to far less radiation than x-rays do. One such scan called dimercaptosuccinic acid (DMSA) scintigraphy first employs injections of tiny amounts of radioactive tracing medicine. A scanning machine (scintillation or gamma camera) is then used to detect pictures of the tracer in the kidney. This information is recorded on a computer screen or on film.

Magnetic Resonance Imaging (MRI) or Computed Tomography (CT). Magnetic resonance imaging (MRI) and computed tomography (CT) scans are noninvasive advanced imaging techniques that are sometimes used when nuclear scans are inconclusive. A CT scan is useful for ruling out kidney stones or obstructions in women with recurrent UTIs.

X-Rays. Special x-rays can be used to screen for structural abnormalities, urethral narrowing, or incomplete emptying of the bladder, which can cause stagnation of urine and predispose to infection.

  • Voiding cystourethrogram is an x-ray of the bladder and urethra. To obtain a cystourethrogram, a dye, called contrast material, is injected through a catheter inserted into the urethra and passed through the bladder.
  • An intravenous pyelogram (IVP) is an x-ray of the kidney. For a pyelogram, the contrast matter is injected into a vein and eliminated by the kidneys. In both cases, the dye passes through the urinary tract and reveals any obstructions or abnormalities on x-ray images. Due to the possible risks to the fetus, x-rays are not performed on pregnant women.
Voiding cystourethrogram Click the icon to see an image of a voiding cystourethrogram.
Intravenous pyelogram (IVP) Click the icon to see an image of an intravenous pyelogram.

Cystoscopy. Cystoscopy is used to detect structural abnormalities, interstitial cystitis, or masses that might not show up on x-rays during an IVP. The patient is given a light anesthetic and the bladder is filled with water. The procedure uses a cystoscope, a flexible, tube-like instrument that the urologist inserts through the urethra into the bladder.

Cystoscopy Click the icon to see an image of cystoscopy.

Other Diagnostic Tests for Kidney Infections and Severe UTIs

No noninvasive test will differentiate between upper and lower urinary tract infections. This is a particular problem because of the high percentage of women whose cystitis symptoms mask infections that also exist in the upper tract.

Antibiotic Trial. The best current test for pyelonephritis is the short-term antibiotic therapy given for cystitis. If the infection returns within two weeks after treatment, upper urinary tract infection is usually present.

Blood Cultures. If symptoms are severe, blood cultures will be taken to determine if the infection is in the bloodstream and threatening other parts of the body.


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