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Common Test For Bladder Infections Misses Too Many Cases

Urine tests are the gold standard for diagnosing bladder infections. But one common test, the urine culture, can easily miss infections.
Ian Hooton
Urine tests are the gold standard for diagnosing bladder infections. But one common test, the urine culture, can easily miss infections.

Most women know all too well the pain and discomfort of a urinary tract infection. They also know they'll probably have to trek to the doctor for a urine analysis so they can get a prescription for antibiotics.

Surely there's got to be a better way.

The first step for women with a history of urinary tract infections may be skipping a standard test isn't that good at spotting bladder infections anyway.

"Fewer tests should be done," says Dr. Michael Donnenberg, a professor of medicine at The University of Maryland School of Medicine who wasn't involved in the study. "It's even a poorer test than we thought."

Urinary tract infections lead to 8 million doctor visits a year, according to the Centers for Disease Control and Prevention. That adds up to plenty of expense and inconvenience that in many cases may not be worth the trouble.

Doctors have two choices for urine tests: the dipstick test, which gives near-instant results and is useful for ruling out infection, and the urine culture. That is done in a lab and takes one to three days.

The urine culture, formally called a midstream urine culture, accurately identified most women who had bladder infections with E. coli bacteria, which cause at least three-quarters of infections, the study found.

But the test missed women who had infections with other bacteria, or had low levels of E. coli that were still enough to make the women sick.

Many labs ignore those low-level tests, says Dr. Thomas Hooten, a professor at the University of Miami School of Medicine who led the study.

If doctors are going to do urine cultures they should at least insist that labs look for low levels of E. coli, Hooten says. He told Shots that he would say: "Look guys, low colony counts of E. coli are meaningful, don't discard those results."

The results were just published in the New England Journal of Medicine.

The study involved 226 women, aged 18 to 49, and got samples both from the midstream test and by putting a catheter in the bladder.

When comparing those samples, something strange showed up, surprising the doctors.

About one-quarter of the women had no bacteria at all in the bladder, even though they had classic symptoms of infection. And quite a few of those women did have lots of bacteria in their midstream test.

"We would have assumed that the reason you had high numbers in the midstream culture is because they had high numbers in the bladder," says Donnenberg, who wrote an editorial accompanying the study.

Maybe those women have an infection of the urethra rather than the bladder, Donnenberg told Shots, or maybe there's something else going on that the doctors weren't aware of. The doctors really don't know.

"I don't know if they're benefiting from treatment because they really have bacterial urethritis, or if they're being exposed unnecessarily to antibiotics," Donnenberg says.

OK, this is all very interesting, but how is it going to help a woman who thinks she probably has a UTI? Like, uh, right now?

Unfortunately, doctors don't have a more accurate test to replace the urine culture.

As a result, doctors have become increasingly comfortable with prescribing antibiotics without doing a urine culture, Donnenberg says, and this study supports doing that for healthy female patients. "If their physician doesn't do cultures, that should not make them uneasy."

Going for a urine culture is often a good idea the first time a woman has UTI symptoms, Donnenberg says, to make sure the symptoms aren't caused by the sexually transmitted diseases chlamydia or gonorrhea instead.

"But once a woman knows it's a UTI because she's had a few, calling up the doctor and saying, 'I have another one, can I have a prescription?' is fine."

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