What is a Pap smear test?
The Pap smear is a test that checks for changes in the cervix that may become cancer. If a Pap smear shows these changes, the result is called abnormal. In women who have regular Pap smears, abnormal changes are almost always caught very early. An abnormal Pap smear result may mean that further testing and follow-up are needed.
Detecting cervical problems
These abnormal cells show early pre-cancer changes called dysplasiaor cervical intraepithelial neoplasia (CIN). Dysplasia and CIN are graded as mild, moderate, or severe. Mild dysplasia (CIN 1) usually goes away on its own. Moderate (CIN 2) and severe (CIN 3) dysplasia indicate more serious changes.
The Pap smear checks for abnormal changes in the cells of the cervix and allows early treatment so that they do not become cancer. Regular use of the Pap smear has greatly reduced the number of cases of cervical cancer in Australia.
HPV and abnormal Pap smear result
The main cause of abnormal Pap smear results is infection with human papillomavirus (HPV). There are many types of HPV. Some types have been linked to cancer of the cervix, vulva, and vagina. Other types have been linked to genital warts.
HPV infection is very common, especially in women younger than 20 years. It is passed from person to person through sexual contact. Usually, a woman’s immune system clears the virus quickly, and the infection goes away by itself. But in some women, HPV does not go away quickly. A small number of these women will go on to develop CIN. The longer HPV is present and the older the woman, the greater the risk she will develop CIN. Smoking doubles the risk of CIN 3 when HPV is present. However, it usually takes years for pre-cancer changes in the cervix to cause cervical cancer.
Pap smear results: The Bethesda System
The terms used to describe an abnormal Pap smear result can be confusing. Most laboratories use the “Bethesda System” to describe Pap smear results. This system uses the term squamous intraepithelial lesion (SIL) to describe pre-cancer changes. “Squamous” refers to the type of cells that make up the tissue that covers the cervix. With this system, the results will be placed in one of several groups:
- Normal (negative) – There are no signs of cancer or pre-cancer.
- Atypical squamous cells of undetermined significance (ASC–US) -Changes in the cervical cells have been found. The changes are almost always a sign of an HPV infection but may indicate pre-cancer is present. ASC-US is the most common abnormal Pap smear result.
- Squamous intraepithelial lesion (SIL) – Abnormal changes are seen in the cells that may be a sign of pre-cancer. SIL can be low grade (LSIL) or high grade (HSIL). These grades are related to the grades of dysplasia and CIN. LSIL almost always indicates that an HPV infection is present, but it also may indicate mild pre-cancer changes. LSIL is very common and usually goes away on its own without treatment. HSIL indicates more serious changes. Carcinoma in situ (CIS) is a severe form of HSIL. It is the result most likely to progress to cancer.
- Atypical squamous cells, cannot exclude HSIL (ASC-H) – Changes in the cervical cells have been found. These changes are not clearly HSIL but could be. Further testing is needed.
- Atypical glandular cells (AGC) – Cell changes are seen that suggest pre-cancer of the upper part of the cervix or uterus.
- Cancer – Abnormal cells may have spread deeper into the cervix or to other tissues.
Further testing following an abnormal Pap smear result
An abnormal Pap smear result may need further testing. The follow-up that is received after an abnormal Pap smear result depends on your age and the grade of dysplasia. Sometimes, there is more than one option for further testing:
Repeat Pap smear
For some women, one further testing option is to repeat the Pap smear a few months later. This may give time for the changes to resolve on their own. For women 21 years and older with ASC–US, the test is given every 6 months until she has two normal results. She then can return to the routine Pap smear schedule. For women 20 years and younger with ASC–US or LSIL, the Pap smear is repeated in 1 year.
Another option for some women is an HPV test. This test detects the presence of cancer-causing types of HPV in cervical cells. The cells used for the initial Pap test often can be tested, so a woman does not need to return to the office for another test.