A while ago, I had a Pap test that showed precancerous cells. I did not find this out until six months after my exam because I had left town. When I came back and heard this, I had another Pap done, and this time the results were normal. How could this have happened? Did my body heal itself? Or was it possible that there was a mistake the first time? If so, how often does that happen? Or could the second test be mistaken?

C.

There are several classes of abnormalities on Pap smears: atypical cells of undetermined significance; low-grade lesions (mild dysplasia); and high-grade lesions (moderate or severe dysplasia). Almost 60 percent of the time, mild dysplasia will return to normal even without treatment. Moderate dysplasia reverts to normal about 40 percent of the time, but severe dysplasia only occasionally gets better without intervention.

When there is an abnormality on a Pap smear, especially a high-grade lesion, a colposcopy is usually recommended. This test enables the doctor to look directly at the cervix with a microscope and to take a biopsy of any areas that appear abnormal. A biopsy is more conclusive than a Pap smear, so any treatment decisions are based on results of a colposcopy and biopsies, not on the Pap alone.

There is about a 10 percent incidence of false-negative results (meaning the Pap smear comes back normal when there really is an abnormality) and false positives can occur as well. If one has a mildly abnormal Pap, often a repeat Pap smear in six months is the only recommendation. If a repeat Pap smear is normal, then Paps are recommended every six months for a year. If subsequent Pap smears are normal, one can return to a once-a-year schedule, but if there are more abnormal Paps, a colposcopy is done.