A doctor or health provider performs a Pap smear primarily to look for cervical and/or vaginal cells that are cancerous or that may be pre-cancerous. A sample of cervical cells or cell suspension is placed on a glass slide, stained with a special dye (Pap stain), and viewed under a microscope by a cytotechnologist or pathologist. The Pap test can also be used to detect vaginal or uterine infections.
Abnormal cells and infections can be present without causing any noticeable symptoms. In some cases, further testing and/or treatment may be required while in other cases, the doctor may choose to monitor the person over time to see if the situation resolves on its own.
Some strains of human papillomavirus (HPV), a very common sexually transmitted viral infection, can be associated with an increased risk of cervical cancer. A doctor may also order an HPV DNA test along with or following a Pap smear, especially for women age 30 to 65.
The appropriate frequency of Pap testing is dependent on age, concurrent use of the HPV DNA test, and risk factors (see Screening: Cervical Cancer (Young Adults), (Adults), (Adults 50 and Up)). The American College of Obstetricians and Gynecologists (ACOG), the U.S. Preventive Services Task Force (USPSTF), and the American Cancer Society recommend the following:
Screening with Pap smears should begin no earlier than age 21.
Women between the ages of 21 and 30 should have a Pap smear every 3 years.
Women between the ages of 30 and 65 should have both a Pap smear and an HPV test every 5 years (preferable); a Pap test alone every 3 years is also acceptable.
After age 65, no screening is necessary if women have had adequate prior screening and no history of cervical cancer. Adequate prior screening has been defined as 3 consecutive negative Pap smears or 2 consecutive negative HPV DNA tests within the last 10 years, with the most recent within the last 5 years.
Some women may need more frequent screening. Women with the following conditions and circumstances should discuss shorter screening intervals with their doctors:
A "negative" Pap smear means the cells obtained appear normal or there is no identifiable infection. In some instances, the conventional Pap smear may be reported as "unsatisfactory" for evaluation. This may mean that cell collection was inadequate or that cells could not be clearly identified. A summary of other reported results follows. [See also Pap Smear Terminology on the 2001 Bethesda System for classification of Pap smear results.]
Unsatisfactory: inadequate sampling or other interfering substance
Benign: non-cancerous cells, but smear shows infection, irritation, or normal cell repair
Atypical cells of uncertain significance: abnormal changes in the cells that cover most of the external part of the cervix (squamous cells-ASCUS) or in the cells that cover the lining of the uterus opening and canal (glandular cells—AGCUS) for which the cause is undetermined; an ASCUS test result is frequently followed up with DNA testing to identify the presence of a high-risk infection with HPV.
Low-Grade changes: frequently due to infection with HPV, which in some instances can be a risk for cervical cancer; this test result may be followed up with DNA testing to identify the presence of a high-risk HPV infection [see HPV DNA].
High-Grade changes: very atypical cells that may result in cancer
Squamous cell carcinoma or adenocarcinoma: terms used to identify certain types of cancer; in these cases, cancer is evident and requires immediate attention.
The Pap smear is generally used as a screening test. A certain percentage of abnormalities in women may go undetected with a single Pap smear, which is why it is important to have Pap smears done regularly. A significant limitation of the test has to do with sample collection. The Pap smear represents a very small sample of cells present on the cervix and in the vaginal area. Even for the most experienced physician, sample collection can be occasionally inadequate and a repeat Pap may be required.
If a woman douches, tub bathes, or uses vaginal creams 48 to 72 hours prior to the examination, the test results might be "unsatisfactory." Other factors that may alter results include menstrual bleeding, infection, drugs (such as digitalis and tetracycline), or having sexual relations within 24 hours prior to examination.
In these cases, a repeat Pap smear may be necessary, but it does not necessarily mean there is a significant problem. In some instances, the use of the liquid-based techniques may eliminate obscuring materials such as blood and mucus that may prevent a clear and uncluttered presentation of cervical cells. A second advantage is that the same sample may be used to perform additional testing for HPV, if appropriate.
This article was last reviewed on June 11, 2012. | This article was last modified on March 27, 2015.
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