The American College of Obstetricians and Gynecologists recommends that a Pap smear be done for all women by age 18 or who are sexually active, regardless of age. Women who have multiple sexual partners should be screened annually, but those in long-term, stable relationships who have had negative Pap smears three years in a row may be screened less often.
A major problem with the Pap smear is that it is often thought to be normal when it is actually abnormal. The pathologist examining the cells can make an error, the health care provider may not sample the cervix adequately or an infection might obscure the results. The estimated false negative rate is about 20 percent, half of which can be attributed to faulty sampling techniques.
Adenocarcinomas and adenosquamous carcinomas are also more difficult to detect on Pap smears since they start high up in the cervical canal and may not be sampled by the Pap smear. Because of the high false negative rate, routine annual screening is strongly recommended to decrease the likelihood that cervical warts, dysplasia or cancer will be missed.
