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Questions and Answers About the Pap Test
Date reviewed: 8/1/2001
1. What is a Pap test?
The Pap test (sometimes called a Pap smear) is a way to examine cells collected from the cervix (the lower, narrow end of the uterus). This test can show the presence of infection, inflammation, abnormal cells, or cancer.
What is a pelvic exam?
In a pelvic exam, the uterus, vagina, ovaries, fallopian tubes, bladder, and rectum are felt to find any abnormality in their shape or size. During a pelvic exam, an instrument called a speculum is used to widen the vagina so that the upper portion of the vagina and the cervix can be seen.
Why are a Pap test and pelvic exam important?
A Pap test and pelvic exam are important parts of a woman's routine health care because they can detect abnormalities that may lead to invasive cancer. These abnormalities can be treated before cancer develops. Most invasive cancers of the cervix can be prevented if women have Pap tests and pelvic exams regularly. Also, as with many types of cancer, cancer of the cervix is more likely to be treated successfully if it is detected early.
Who performs a Pap test?
Doctors and other specially trained health care professionals, such as physician assistants, nurse midwives, and nurse practitioners, may perform Pap tests and pelvic exams. These individuals are often called clinicians.
How is a Pap test done?
A Pap test is simple, quick, and painless; it can be done in a doctor's office, a clinic, or a hospital. While a woman lies on an exam table, the clinician inserts a speculum into her vagina to open it. To do the test, a sample of cells is taken from in and around the cervix with a wooden scraper and/or a small cervical brush. The specimen (or smear) is placed on a glass slide and preserved with a fixative, or is rinsed in a vial of fixative, and is sent to a laboratory for examination.
Who should have Pap tests?
Current guidelines recommend that women who are or have been sexually active, or have reached age 18, should have Pap tests and pelvic exams regularly. Women may want to discuss with their doctor how often to have the test.
There is no known age at which Pap tests cease to be effective. Women who have had consistently normal Pap test results may want to ask their doctor how often they need to have a Pap test.
Women who have had a hysterectomy (surgery to remove the uterus) should talk with their doctor about whether to continue to have regular Pap tests. If the hysterectomy was performed for the treatment of cancer or a precancerous condition, the end of the vaginal canal still needs to be sampled for abnormal changes. If the uterus (including the cervix) was removed because of a noncancerous condition such as fibroids, routine Pap tests may not be necessary. Women who have had a supracervical hysterectomy (removal of the uterus but not the cervix) should continue to have regular Pap tests. It is important for all women who have had a hysterectomy to have regular gynecologic examinations as part of their health care.
When should the Pap test be done?
A woman should have this test when she is not menstruating; the best time is between 10 and 20 days after the first day of the last menstrual period. For about 2 days before a Pap test, she should avoid douching, or using vaginal medicines or spermicidal foams, creams, or jellies (except as directed by a physician). These may wash away or hide abnormal cells.
How are the results of a Pap test reported?
Most laboratories in the United States now use the Bethesda System to report Pap test results. The Bethesda System uses descriptive terms rather than class numbers, which were used to report Pap test results in the past. The Bethesda System includes an evaluation of specimen adequacy and divides cervical cell abnormalities into three major categories:
- ASCUS-atypical squamous cells of undetermined significance. Squamous cells are the thin flat cells that form the surface of the cervix.
- LSIL-low-grade (early changes in the size and shape of cells) squamous intraepithelial lesion. The word lesion refers to an area of abnormal tissue; intraepithelial means that the abnormal cells are present only in the surface layer of cells.
- HSIL-high-grade squamous intraepithelial lesion. High-grade means that there are more marked changes in the size and shape of the abnormal (precancerous) cells that look very different from normal cells.
ASCUS and LSIL are considered mild abnormalities. HSIL is more severe and has a higher likelihood of progressing to invasive cancer.
How common are Pap test abnormalities?
About 50 million Pap tests are performed each year in the United States with
5 to 7 percent reported as abnormal. A rough estimate puts the number of ASCUS diagnoses at 2,000,000 per year. An additional 1,250,000 women per year are diagnosed with squamous intraepithelial lesion (SIL) or cervical intraepithelial neoplasia (CIN). Of these women, between 200,000 and 300,000 are diagnosed with the more severe abnormality, HSIL.
What do abnormal results mean?
A physician may simply describe Pap test results to a patient as "abnormal." Cells on the surface of the cervix sometimes appear abnormal but are not cancerous. It is important to remember that abnormal conditions do not always become cancerous, and some conditions are more likely to lead to cancer than others. A woman may want to ask her doctor for specific information about her Pap test result and what the result means.
There are several terms that may be used to describe abnormal results.
- Dysplasia is a term used to describe abnormal cells. Dysplasia is not cancer, although it may develop into very early cancer of the cervix. In dysplasia, cervical cells undergo a series of changes in their appearance. The cells look abnormal under the microscope, but they do not invade nearby healthy tissue. There are three degrees of dysplasia, classified as mild, moderate, or severe, depending on how abnormal the cells appear under the microscope.
- Squamous intraepithelial lesion (SIL) is another term that is used to describe abnormal changes in the cells on the surface of the cervix. The word squamous describes cells which are thin, flat, and form the outer surface of the cervix. The word lesion refers to abnormal tissue. An intraepithelial lesion means that the abnormal cells are present only in the surface layers of the cells. A doctor may describe SIL as being low-grade (early changes in the size, shape, and number of cells) or high-grade (precancerous cells that look very different from normal cells).
- Cervical intraepithelial neoplasia (CIN) is another term that is sometimes used to describe abnormal cells. Neoplasia means an abnormal growth of cells.
Intraepithelial refers to the surface layers of the cells. The term CIN, along with a number (1 to 3), describes how much of the thickness of the lining of the cervix contains abnormal cells.
- Atypical squamous cells of undetermined significance (ASCUS) is a term used to describe abnormalities that do not fulfill the criteria for SIL, CIN, or dysplasia. An estimated 5 to 10 percent of patients with ASCUS who undergo further evaluation have HSIL or, rarely, invasive cancer. Persistent abnormal Pap test results are often further evaluated with a repeat Pap test or other tests by a clinician.
- Carcinoma in situ describes a pre-invasive cancer that involves only the surface cells and has not spread into deeper tissues.
Cervical cancer, or invasive cervical cancer, occurs when abnormal cells spread deeper into the cervix or to other tissues or organs.
How do these terms compare?
- Mild dysplasia may also be classified as LSIL or CIN 1.
- Moderate dysplasia may also be classified as HSIL or CIN 2.
- Severe dysplasia may also be classified as HSIL or CIN 3.
- Carcinoma in situ may also be classified as HSIL or CIN 3.
How are human papillomaviruses (HPVs) associated with the development of cervical cancer?
Human papillomaviruses are a group of more than 100 viruses. Some HPVs are sexually transmitted and cause wart-like growths on the genitals. More than a dozen of these HPVs have been linked to cervical cancer. Other types of HPV cause the common warts that grow on hands and feet. These types do not lead to cancer.
HPV infection is the primary risk factor for cervical cancer. However, although HPV infection is very common, only a very small percentage of women infected with untreated HPV are at risk of developing cervical cancer.
Who is at risk for HPV infection?
HPV infection is more common in younger age groups, particularly among women in their late teens and twenties. Because HPV is spread mainly through sexual contact, risk increases with number of sexual partners. Women who become sexually active at a young age, who have multiple sexual partners, and whose sexual partners have other partners are at increased risk. Women who are infected with the human immunodeficiency virus (HIV) are also at higher risk for being infected with HPV and for developing cervical cancer. Nonsexual transmission of HPV is rare. The virus often disappears but sometimes remains detectable for years after infection.
Does infection with a cancer-associated type of HPV always lead to a precancerous condition or cancer?
No. Most HPV infections appear to go away on their own without causing any kind of abnormality. However, persistent infection with cancer-associated HPV types may increase the risk that mild abnormalities will progress to more severe abnormalities or cervical cancer. With regular followup care by trained clinicians, women with precancerous cervical abnormalities can be treated before cancer develops.
What are false positive and false negative results?
Unfortunately, there are occasions when Pap test results are not accurate. Although false positive and false negative results do not occur very often, they can cause anxiety and can affect a woman's health.
A false positive Pap test occurs when a patient is told she has abnormal cells, but the cells are actually normal. A false negative Pap test occurs when a specimen is called normal, but the woman has a lesion. A variety of factors may contribute to a false negative result. A false negative Pap test may delay the diagnosis and treatment of a precancerous condition. However, regular screening helps to compensate for the false negative result. If abnormal cells are missed at one time, chances are good that the cells will be detected the next time.
What methods are being developed to improve the accuracy of Pap tests?
In April 1996, the Consensus Development Conference of Cancer of the Cervix, which was convened by the National Institutes of Health (NIH), concluded that about half of the false negative Pap tests are due to inadequate specimen collection. The other half are due to a failure to identify or interpret the specimens correctly. Although the conventional Pap test is effective in the majority of cases, the conference made it clear that new methods of collecting specimens and reading cervical cells are needed to reduce the number of false negatives.
One new method, called liquid-based thin-layer slide preparation, may make it easier to screen for abnormal cells. Cervical cells are collected with a brush or other collection instrument. The instrument is rinsed in a vial of liquid preservative. The vial is sent to a laboratory, where an automated thin-layer slide device prepares the slide for viewing. Preliminary results of this method suggest that it is comparable to, or more sensitive than, Pap tests for the detection of significant abnormalities.
Computer automated readers are also being used to improve the reading of Pap tests. This technology uses a microscope that conveys a cellular image to a computer, which analyzes the image for the presence of abnormal cells.
How can a woman find out whether her Pap test is accurate?
It is important for a woman to discuss the results of her Pap test with her doctor and to ask about the quality control measures that were taken in the laboratory where her sample was evaluated.
What if Pap test results are abnormal?
If the Pap test shows an ambiguous or minor abnormality, the physician may repeat the test or perform a test for HPV to determine whether further followup is needed. If the Pap test shows a significant abnormality, the physician may then perform a colposcopy using an instrument much like a microscope (called a colposcope) to examine the vagina and the cervix. The colposcope does not enter the body. A Schiller test may also be performed. For this test, the doctor coats the cervix with an iodine solution. Healthy cells turn brown and abnormal cells turn white or yellow. Both of these procedures can be done in the doctor's office.
The doctor may also remove a small amount of cervical tissue for examination by a pathologist. This procedure is called a biopsy and is the only sure way to know whether the abnormal cells indicate cancer.
Findings of the ASCUS/LSIL Triage Study (ALTS), a major clinical trial (research study) funded and organized by the National Cancer Institute (NCI), suggest that HPV testing in women with ASCUS Pap test results may help identify underlying abnormalities that need a doctor's attention. The study results suggested that testing cervical samples for HPV can identify most ASCUS abnormalities that need treatment. A negative HPV test can provide reassurance that cancer or a precancerous condition is not present. Analysis of results from the ALTS is ongoing.
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