A Pap test is primarily used to screen for cervical cancer. It is used to look for cervical and/or vaginal cells that are cancerous or that may be precancerous. 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 and/or pathologist. The Pap test can also be used to detect vaginal or uterine infections, such as trichomonas 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 healthcare provider may choose to monitor the person over time to see if the situation resolves on its own.

Almost all cases of cervical cancer are caused by persistent infections with certain strains of human papillomavirus (HPV), a very common sexually transmitted viral infection. An HPV DNA test may be done along with a Pap test for women age 30 to 65 every 5 years. Abnormal results on a Pap test may also be followed by HPV testing.

Recent (2015) interim guidelines from a panel of experts representing several major health organizations say that HPV testing without a Pap test may be offered as a cervical cancer screening option for women age 25 and older. (For more on this, see Common Questions #2 and the news item "Experts Offer Advice on hrHPV Testing as a Primary Screen for Cervical Cancer.")

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, the U.S. Preventive Services Task Force, and the American Cancer Society recommend the following:

• Screening with Pap tests should begin no earlier than age 21.
• Women between the ages of 21 and 30 should have a Pap test every 3 years.
• Women between the ages of 30 and 65 should have both a Pap test 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. This means that a woman who has had 3 consecutive negative Pap tests or 2 consecutive negative HPV DNA tests within the last 10 years, with the most recent within the last 5 years, no longer needs screening once she turns 65 years old.

The recent interim guidelines on using HPV testing without a Pap test suggest that women who choose this option and have a negative result on an initial HPV test not be screened again for 3 years.

Some women may need more frequent cervical cancer screening. Women with the following conditions and circumstances should discuss shorter screening intervals with their healthcare provider:

• HIV infection
• Suppressed immune system for other reasons, such as organ transplant
• Exposure to DES (diethylstilbestrol) during their mothers' pregnancy
• Previous treatment for cervical cancer or a condition called cervical intraepithelial neoplasia-2 or 3 (CIN 2, CIN 3)

A health practitioner may also order a Pap test when a woman has multiple sexual partners, is pregnant, or has abnormal vaginal bleeding, pain, sores, discharge, or itching.

A "negative" Pap test means the cells obtained appear normal or there is no identifiable infection. In some instances, the conventional Pap test 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 Test Terminology on the Bethesda System for classification of Pap test results.]

• Unsatisfactory: inadequate sampling or other interfering substance
• Benign: non-cancerous cells, but test 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 HPV 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.
• 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 test is generally used as a screening test. A certain percentage of abnormalities in women may go undetected with a single Pap test, which is why it is important to have Pap test done regularly. A significant limitation of the test has to do with sample collection. The Pap test represents a very small sample of cells present on the cervix and in the vaginal area. Even for the most experienced health practitioner, 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 test 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.