The Pap test - Introduction and results
This article was reviewed and updated on August 5, 2019.
by Adnan Karavelic, MD FRCPC
The Pap test is a screening test that looks for abnormal cells in the cervix.
The purpose of the Pap test is to look for pre-cancerous diseases but cancers may also be identified.
Most pre-cancerous diseases and cancers in this area are caused by a virus called human papillomavirus (HPV).
You should discuss any abnormal results with you doctor who may recommend additional tests.
This article will provide an introduction to the Pap test and possible test results. Continue reading to learn more.
The normal cervix and uterus
The uterus is a pear-shaped, hollow, female reproductive organ located in the small pelvis. The upper part of the uterus is called the body (uterine corpus), and the lower part is called the neck (uterine cervix). The body is made up of muscles that form a cavity called the endometrium. The endometrium is lined by endometrial glands and stroma.
The uterine cervix is found at the top of the vagina. A narrow passage that runs through the cervix and connects the endometrium and the vagina is called the endocervical canal.
The endocervical canal is covered by a different kind of cell that connect to form endocervical glands.
The endometrium is also covered in glands that change throughout the menstrual cycle. The tissue in between the glands is called stroma.
What is a Pap test?
The Pap test (Pap smear, cervical smear) is a screening test that looks for abnormal cells in the vaginal portion of the uterine cervix. It is called a screening test because it is designed to detect disease before a person experiences any symptoms. The test was named after Dr. Georgios Papanicolaou who invented the test with Dr. Aurel Babes in the early 20th century.
Why is Pap test performed?
The purpose of the Pap test is to look for pre-cancerous diseases in the cervix. These pre-cancerous diseases can turn into cancer over time, so it is important to find and treat them early. The Pap test can also identify abnormal cells coming from the endocervical canal or endometrium.
The most common cancer in the cervix is squamous cell carcinoma. This type of cancer develops from a pre-cancerous disease called high grade squamous intraepithelial lesion (HSIL). The Pap test is designed to look for both squamous cell carcinoma and HSIL.
The Pap test can also identify infection causing microorganisms including:
What causes cervical cancer?
Most cancers and pre-cancerous diseases in the cervix are caused by a virus called human papillomavirus (HPV). The virus infects cells on the surface of the cervix which causes them to change over time into cancer cells. The same virus causes cancers and pre-cancerous diseases in other parts of the body including the throat, anal canal, vulva, and penis.
How is the Pap test performed?
A Pap test is usually performed in a doctor’s office by a family physician, a gynecologist, or a trained nurse. You will be asked to lay down on your back on an examination table with your knees bent. The doctor will use a medical device called a speculum to see your cervix. Small samples of tissue will then be taken from your cervix using a soft brush and a scraping device called a spatula. For most patients the procedure only takes a couple minutes.
Who should get tested?
Screening with the Pap test should start at the age of 21 for sexually active women. For women that have never been sexually active, the screening should be delayed until they are sexually active. Sexual activity includes intercourse, as well as digital or oral sexual activity involving the genital area with a partner of either sex. If no abnormal cells are detected, the test should be repeated every 3 years. A woman may choose to discontinue screening at age 70 if all her tests over the previous 10 years were negative.
The Pap test is safe and effective even if you are pregnant. Pregnant women should be screened according to the same guidelines as non-pregnant women. Women who have had their uterus removed and transgender men who still have a cervix, should be screened according to the same guidelines. Women who are immunocompromised (HIV+, immunosuppressant therapy, autoimmune disease) should have a Pap test performed every year.
In some situations, the Pap test may be used to obtain a sample from the vagina, since the vaginal walls are lined by the same type of cells as the vaginal potions of the uterine cervix. The same pre-cancerous conditions can be detected in the vagina.
*These recommendations are based on Ontario Cervical Screening Guidelines. Other provinces may have slightly different guidelines.
What are the possible Pap test results?
In Canada and the United States, the results of a Pap test are divided into three categories:
Normal (negative for intraepithelial lesion or malignancy)
If your pap smear is normal, your result will say negative for intraepithelial lesion or malignancy. Normal cells need to be seen in order to make this diagnosis. Your doctor will schedule the next routine Pap test according to the local guidelines.
The abnormal category includes both pre-cancerous and cancerous diseases. It also includes some results that are considered preliminary. This means that your pathologist saw something abnormal after examining your tissue under the microscope but that there were not enough cells to make a final diagnosis.
The following is a list of possible abnormal results:
Why is this important? A cancer result requires immediate treatment. Contact your doctor if you receive a cancer result and do not receive information regarding the next steps in a timely manner.
Why is this important? The risk of cancer is higher for patients with HSIL. If you receive a result of HSIL, your doctor will discuss possible treatment options with you. The risk of cancer is lower for patients with LSIL although your doctor will talk with you about performing a second Pap test.
Preliminary result (not a final diagnosis)
Atypical squamous cells, cannot rule out high-grade squamous intraepithelial lesion (ASC-H).
Atypical endocervical cells, not otherwise specified (NOS).
Atypical endometrial cells, not otherwise specified (NOS).
Atypical endocervical cells, favour neoplastic.
Why is this important? You should talk with you doctor about any of the above preliminary abnormal results. In most situations, additional tests or a repeat Pap test will be recommended.
In rare situations, the results of a Pap test might be described as inadequate. This means that your pathologist could not reach a diagnosis based on the tissue received for examination. Common reasons for this include small number of cells, poor preservation of cells, obstructing elements such as blood, and tissue processing errors.
Why is this important? A repeat Pap test is usually performed when the result is inadequate.
Cells from inside the endometrial cavity (the endometrium) may be seen in your tissue sample. This result is considered normal in women under the age of 45. However, for women over the age of 45 years, these cells are potentially abnormal.
Why is this important? If you are over 45 years of age and endometrial cells are seen on your Pap smear, your doctor may recommend additional tests. The tests may include taking a small sample of tissue from the inside of your uterus in a procedure called an endometrial biopsy.