The Pap test is a medical screening test that is designed to check for the early warning signs of cancer of the uterine cervix.
It was first described by George Papanicolaou and is also sometimes known as the Papanicolaou test, Pap smear, cervical smear, cervical cytology or simply a smear test.
Although the Pap smear is primarily used for the detection of abnormalities of the cervix, it may also sometimes indicate the presence of infections of the vagina and the cervix and may also sometimes indicate the presence of cancer cells that originate from the lining of the uterus or the endometrium. However, the test was not designed for this purpose.
What is the aim of a Pap test?
The cervix is that portion of the uterus that is partly visible to a doctor during a pelvic examination. The outer part of the cervix is called the ecto-cervix and contains on its surface a certain type of cell that looks very much like a paving stone. These flat cells are called squamous cells. Slightly higher up in the cervix a different type of cell is found that is more upright and produces mucus. These are called endo-cervical cells.
Where the two different types meet, there is a special area called the transformation zone where one cell type may change into another cell type under the influence of hormones. This transformation zone is very sensitive to the influence of cancer-causing agents and that is the reason why the most common cancer of women in South Africa (cervix cancer) occurs exactly at this part of the body.
The Pap test is a medical investigation where cells from the cervix are taken during a pelvic examination. The doctor will insert a special instrument (speculum) into the vagina to keep the walls apart in order to better see the cervix. A wooden/plastic spatula or brush is used to gently scrape off some of the cells of the cervix, which are then smeared on to a glass slide that is marked with the patient's name and identification number. These cells are then fixed on to the slide with a spray. The glass slide is transported to a laboratory where the cells are stained with pigments in order to highlight certain features.
What is the cause of abnormal cells on the cervix?
Abnormal cells on the cervix may predict the development of cancer many years before the event. The abnormal cells display certain characteristics that indicate damage and are usually classified according to the Bethesda system in South Africa (see description of results).
It is now known that human papillomavirus (HPV) infection is an important risk for the formation of dysplastic cells (abnormal cells) on the cervix. There are different types of HPV, and certain types are more likely to cause cancer. These types are called the oncogenic types and can be found in nearly all cases of cervix cancer. Other risk factors for the development of abnormal cells include smoking and low immunity, for instance with HIV infection.
Who should get a Pap test?
All women should get regular Pap smears after the onset of sexual activity. The smear test should be repeated one to three yearly, depending on the advice of the healthcare worker. A Pap smear can be done on any day of the menstrual cycle but sometimes a doctor may ask to postpone the smear test during the heaviest days of the menstrual flow.
However, if bleeding continues, it is important to get the smear test done despite the bleeding because abnormal bleeding may be a sign of cervical cancer. A Pap smear can safely be done during the earlier months of pregnancy (usually up to around 20 weeks) without any risk to the pregnancy.
How are the results reported?
Cervical cytology is not a final diagnosis and is a screening test. It gives an indication of the degree of the abnormality and identifies those patients that need further investigation and treatment. In South Africa the Bethesda system of classification is widely used.
A Pap smear can be reported as normal, low-grade squamous intraepithelial lesion (LSIL) or high-grade squamous intraepithelial lesion (HSIL). Very rarely the Pap smear may indicate a cancer. There are a few other categories of abnormal smears and your doctor will be able to explain these.
The usual advice after a LSIL smear will be to repeat the smear six to twelve months later, and, if the smear is again abnormal, the patient would be referred for further tests. If the smear shows an HSIL or carcinoma, the patient will get an urgent referral for further tests. These tests usually include colposcopy and biopsy (see article on cervical biopsy).
How accurate is a Pap test?
A single Pap smear is not a perfect test. There may be a normal result despite an abnormality on the cervix. For this reason, it is important to get repeated smears regularly to minimise the risk of missing an abnormal lesion on the cervix.
Certain improvements on the technology are now available in certain centres, including liquid-based cytology and HPV testing. Liquid-based cytology uses a clear liquid to store that sample instead of a glass slide, and it is a more accurate way to diagnose abnormalities. A test for specific HPV infections can sometimes improve the accuracy of the Pap smear, and may help to determine the risk associated with an abnormal smear.
What happens after a Pap test?
There may be slight bleeding after a Pap smear but it should settle within a day or two. There is usually no pain and after the internal pelvic examination there should be no problems like discomfort or discharge. The results of your Pap smear should be available between three to thirty days after the test, depending on the laboratory.