(AP) -- Too many doctors are testing the wrong women, or using the wrong test, for a virus that causes cervical cancer.
The days of one-size-fits-all screening for cervical cancer are long gone. How often to get a Pap smear - and whether to be tested for the cancer-causing HPV virus at the same time - now depend on your age and other circumstances.
But a government study reports Monday that a surprising number of doctors and clinics aren't following guidelines from major medical groups on how to perform HPV checks, suggesting a lot of women are getting unnecessary tests.
That wastes money and could harm women who wind up getting extra medical care they didn't need, says Dr. Mona Saraiya of the Centers for Disease Control and Prevention, who led the research.
Even she wasn't protected from the confusion. Saraiya was stunned to get a bill showing that her own doctor had ordered testing for HPV strains not connected to cervical cancer.
The findings, reported in the journal Obstetrics & Gynecology, show women have to be savvy to ensure they're getting the right checkups - enough, but not too much.
"It's extremely discouraging," says Debbie Saslow, gynecologic cancer director at the American Cancer Society, who's had to argue with her doctor against testing too often. "We have not been able to get that message across."
Cervical cancer grows so slowly that Pap smears - which examine cells scraped from the cervix - usually find it in time to treat, or even to prevent when precancerous cells are spotted and removed.
For decades, Paps were the only way to screen for cervical cancer. Now doctors know that certain strains of HPV, the human papillomavirus, cause most cervical cancer. HPV testing isn't a replacement for the Pap. But it can provide extra information to help determine if a woman is at higher or lower risk and thus guide her ongoing care - if it's used correctly.
The new CDC study, part of a national survey of medical practices that included 600 providers of cervical cancer screening, examined how doctors are using it.
The study found 60 percent of doctors and clinics say they give a routine Pap-plus-HPV test to women who are too young for that combination. Guidelines stress that so-called co-testing is only for women 30 and older. If both tests are negative, they can wait three years before their next screening.
Why the age limit? Saslow says HPV is nearly as common as the common cold, especially in younger women - but their bodies usually clear the infection on their own and only a years-long infection is risky. Learning that a 20-something has HPV increases the odds of more invasive testing that in turn can leave her cervix less able to handle pregnancy later in life. Younger women are supposed to get HPV testing only if a Pap signals a possible problem and doctors really need the extra information.
Then there's the question of which test to use. Only a few so-called high-risk strains of HPV cause cervical cancer, the strains doctors are supposed to test for. Before scientists understood the different HPV types, a test already was on the market that detects strains that can cause genital warts, not cervical cancer. The CDC's Saraiya says there's no reason to use that old test because learning you have a probably transient warts-causing strain doesn't alter your care.
Yet her study found 28 percent of doctors and clinics say they order tests for both the cancer-causing and warts-causing strains, regardless of patient age. The study couldn't tell why, although Saraiya says some doctors don't know there's a difference and some order forms for the lab tests don't differentiate.
An HPV test costs $80 to $100, on top of a $40 Pap. Saraiya says labs can bill for two HPV tests when doctors order testing for both kinds of strains.
So what does a woman need to know before her next checkup? The CDC has developed a consumer-friendly brochure to help women understand their options for cervical cancer screening: http://tinyurl.com/6g8de6v
And guidelines from the American College of Obstetricians and Gynecologists recommend that:
-Routine Paps start at age 21.
-Most women in their 20s get a Pap every two years.
-Women 30 and older wait three years between screenings if they've had a negative Pap and negative HPV test, or three consecutive clear Paps.
-If a Pap is inconclusive at any age, HPV testing may help rule out who needs further examination and who can just repeat a Pap in a year.
-Anyone who's been vaccinated against HPV, a relatively new vaccine, still must follow Pap screening guidelines for their age group.
-Higher-risk women, such as those with HIV or previous cervical abnormalities, need more frequent screening.
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