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Reviewed by the Faculty of Harvard Medical School

What Your Pap Smear Results Mean

The Pap test (smear) is a screening test used to detect cancer or precancerous changes in the cells of the cervix (the opening to the uterus). Before the Pap smear became widely available in the 1950s, cervical cancer was common and often fatal. Today, deaths from cervical cancer are far less frequent because the Pap smear allows doctors to detect and remove abnormal cells before they turn into cancer.

Pap tests are routinely performed during pelvic examinations. Results usually are available in one to two weeks. Your doctor's office may notify you only if the results are abnormal. You can call the office if you want to confirm that your test is normal. He or she may discuss abnormal results over the phone or you may be asked to come to the office.

The Pap test isn't painful, although women with narrow vaginas or vaginal irritation may experience some slight discomfort. It's normal to have slight bleeding (usually spotting) for a short time after the test.

Understanding The Results

If your doctor tells you the results are abnormal, don't panic. Although this may be a sign of cancer, other conditions, such as inflammation or infection, can cause abnormal results. Even if the test indicates that precancerous cells are present, removing the cells will almost always prevent cancer from developing.

When the Pap smear is examined in the laboratory, the pathologist looks for abnormal cells; that is, cells that are different from healthy cells. Most abnormal cells discovered during Pap smears aren't cancer. However, these cells could turn into cancer if they aren't removed.

The "Bethesda System" is most often used to describe abnormal Pap results. The system first requires that the pathologist determine if there is an adequate sample of cervical cells. If the sample is unsatisfactory, the Pap smear should be repeated. The results will then be categorized as:

  • Negative for intraepithelial lesion or malignancy
  • Atypical cells
  • Low-grade squamous intraepithelial lesion
  • High-grade squamous intraepithelial lesion

Squamous cells are cells that cover the cervix. If the cells on a Pap smear fall into a gray zone where they are not clearly normal or abnormal, they are called atypical. Atypical pap smears are further divided into:

  • "Atypical squamous cells of undetermined significance" (ASC-US), or
  • "Atypical squamous cells, high grade squamous lesion cannot be excluded" (ASC-H).

ASC-US results will usually be followed up by a test for human papilloma virus (HPV) DNA. This test can be performed on the cells obtained for the original pap smear so another visit is not necessary. If the HPV test is negative, the Pap smear should be repeated in 12 months. If the HPV test is positive, colposcopy is recommended.

ASC-H results require further evaluation by colposcopy as described below for low and high grade lesions.

If the cells appear abnormal the Pap test will be read as a low- or high-grade lesion and further evaluations will be advised. Abnormal cells may arise from the cervix, the uterus or the vagina and should be evaluated by colposcopy (see below).

In some cases, the Pap test may reveal that some cells have already become cancerous. An early form of cancer — carcinoma in situ — involves only surface cells and hasn't spread into deeper tissues. A cancer that's spread more deeply into the cervix or to other tissues is called invasive cervical cancer.

Keep in mind that Pap tests aren't perfect. Between 5% and 20% of Pap tests are false negative; that means the Pap test shows just normal cells on the microscope slide even though abnormal cells are present on the cervix. Pap tests are usually performed each year. However, the American Cancer Society has released new guidelines allowing some women to have pap tests every three years. Even though most precancerous changes of the cervix grow slowly, you should expect to have Pap test tests every year unless or until your doctor explains you've qualified for the three-year testing interval.

The Next Step

If cells are only mildly abnormal, your doctor may decide that no treatment is needed. However, you may be advised to return for a repeat Pap smear in three to four months to assure that there is no progression to a more abnormal appearance. Other possible and follow-up procedures include:
  • Colposcopy. Your doctor will apply acetic acid (vinegar) to the cervix, which causes abnormal cells to turn white. Then he or she will examine the area with a magnifying binocular scope. The colposcope allows your doctor to map out areas of the cervix that look abnormal. The abnormal cells seen on the Pap smear probably originate in these regions.
  • Biopsy. Your doctor will remove small samples of tissue from the areas that appear abnormal. It may be mildly uncomfortable for you during the sampling. It provides a larger piece of the cervix for the pathologist to study in the laboratory to determine how severe the lesions are. If the biopsy shows precancerous changes, additional treatment will be advised to remove the abnormal tissue. Several treatment options are available including:
    • Loop electrosurgical excise procedure. A thin, electrically charged wire is used like a scalpel to remove abnormal tissue.
    • Laser excision. Lasers are very accurate and can remove the abnormal cells without damaging healthy surrounding tissue.
    • Cryotherapy. With this procedure cervical cells are destroyed by freezing. It is not often used because it sometimes makes it more difficult to inspect remaining cervical cells during post-treatment follow-up.

Each of these treatments can be done in your doctor's office. Your doctor will numb the area first, so you're unlikely to experience much discomfort. Afterward, you may have cramping or other mild side effects.

The goal of treatment is to remove abnormal tissue, allowing the cervix to heal with normal cells. No treatment is 100% effective, so your cervix will be monitored closely for two years with frequent Pap tests. If your cervix remains normal during the first two years after treatment, you may resume a yearly schedule of screening.

If cancer is already present, your doctor will probably refer you to an oncologist (a cancer specialist) for more advanced treatment.

Last updated October 1, 2010