That's a good question, and apparently one that many physicians aren't answering adequately. As you know, the Pap test, in which cells scraped from the cervix are examined for precancerous changes, has been used for decades and is responsible for an enormous decline in the rates of cervical cancer since the medical community accepted it in 1941.
The HPV test, which looks for infection by the strains of the human papillomavirus known to cause cervical cancer, is newer and very effective, particularly for women 30 and older. Today's cervical cancer screening guidelines call for giving these women both the Pap and HPV tests. If the results of both tests are negative, women can wait three years for their next screening.
HPV is also common in women under 30, but the infections usually clear up quickly in this age range. For that reason, the guidelines call for HPV testing in women under 30 only if a Pap test reveals a problem. Routine Pap testing should start at age 21 for all women, including those who have been vaccinated against HPV.
A five-year National Cancer Institute study reported on more than 330,000 women who underwent both the HPV and Pap tests. The investigators found only about three women in 100,000 developed cervical cancer after negative HPV and Pap tests. It also showed that the HPV tests were twice as good as the Pap tests at predicting the risk of cervical cancer and that if an HPV test was positive, a Pap test could confirm or rule out the need for follow-up or treatment.
But all this good news hasn't changed much. A study from the U.S. Centers for Disease Control and Prevention (CDC) reported in July, 2011 that many doctors aren't following the guidelines, which means that a lot of women are still receiving unnecessary tests. That's a waste of money and, worse, could be harmful if it leads to inappropriate treatment.
The study, published in the July issue of Obstetrics & Gynecology, showed that 60 percent of 376 doctors and 66% of 216 clinics surveyed by the CDC team still routinely screened women under 30 with both the Pap and HPV tests. It also found that 29 percent of doctors who order tests for the cancer-causing HPV strains also check for the strains that cause genital warts. It's not necessary to do both tests. If the test for the strains that can lead to warts is positive, no treatment is needed. (You can't get rid of the virus, but you can have warts removed if any develop.) The only HPV tests needed are for the cancer-causing strains.
Andrew Weil, M.D.