Tuesday, June 14, 2011

What's up with Pap smears, anyway?

Why has the medical community told women for so many years that they need an annual Pap smear? What exactly is a Pap smear and what is it for? Who really needs them and how often? When can you stop getting Pap smears? Why do the recommendations change?

A Pap smear is a test for cervical cancer. The examiner takes a sample of cells from the surface of the cervix and they are stained and examined under a microscope. Most Pap smears are done in asymptomatic patients and are considered screening tests.

The cervix is the portion of the uterus that extends into the vagina. In a “total hysterectomy”, the entire uterus, including the cervix, is removed. In a “partial hysterectomy”, hardly ever done any more, the fundus, or body, of the uterus is removed and the cervix remains. Contrary to popular usage, the difference between a total/partial hysterectomy has nothing to do with whether the ovaries are removed.

When we started doing Pap smears, we knew that cervical cancer was one of the leading cancers in women, but we didn't know what caused it or why some women were more likely to get it than others.

We began to learn more about the epidemiology, or the distribution of cervical cancer in the population. We learned that women who never had vaginal intercourse had very low, although not zero, risk for cervical cancer. It became obvious that risk factors included multiple partners, early age at first intercourse, etc.

Finally, we learned that the presence of human papilloma virus, HPV, was a risk factor for the disease. We further learned that certain subtypes of HPV increased risk and that other subtypes were not associated with increased risk. HPV is sexually transmitted.

So, the initial recommendations were based on incomplete information and these changed as we learned.

When I trained in the late 1980’s, we recommended starting Pap smears following first intercourse or at age 18, whichever came first, and performing them annually after than. When to stop was not defined.

In the early 1990’s, it became clear that we were doing far too many Pap smears.

The recommendation regarding the first Pap smear changed to age 21 because it is very rare to get cervical cancer prior to age 21, no matter what your risk is. This is because progression from the pre-cancerous state to cancer is very slow. The goal is to detect the pre-cancerous state and treat this before cancer develops. There is plenty of opportunity to do this with beginning screening at age age 21.

The same logic (slowly developing pre-cancerous state) supports screening less often than every year. During her 20’s, it is reasonable to screen every other year. After a few negative screens, especially in a low risk woman, it is reasonable to screen every 3 years.

At some point, to be determined by a woman and her physician, screening less often is reasonable. By age 65, a woman in a mutually monogamous relationship with a history of negative screening Pap smears could consider stopping Pap smears altogether. If her situation changes, such as introduction of a new sexual partner, she should consider resuming screening.

At any age, if a woman’s uterus/cervix is removed for benign (non-cancer) reasons she can discontinue Pap smears. This would include hysterectomy for fibroids, pelvic pain, abnormal bleeding, etc. Obviously, if a woman no longer has a cervix, she has no risk for cervical cancer.

Why do some physicians still recommend annual Pap smears? A friend of mine who is an OB/GYN said she recommends them “to get the woman in for her annual exam.” Whether she actually needs an annual exam is fodder for another post.

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