Cervical screening involves women having regular cervical smear tests to check for abnormal cell changes to the cervix (neck of the uterus or womb).

What is a cervical smear test?

A cervical smear test is not a test to look for cancer. It is a screening test that looks for abnormal changes in cells on the surface of the cervix (the neck of the uterus or womb - see diagram). Some cells with abnormal changes can develop into cancer if they are not treated. Treatment of abnormal cells is very effective at preventing cancer.

Women who have regular smear tests every three years as part of a screening programme reduce their risk of developing cervical cancer by about 90 percent. 

It is normal for cells on the surface of the cervix to go through changes. But cells can sometimes change in an abnormal way. Some cells with abnormal changes can become cervical cancer if not treated.

Abnormal cell changes do not cause any symptoms and are picked up only when women have a cervical smear test. Symptoms do not appear until abnormal cells become cancer.

The cervical smear test itself does not prevent cervical cancer. Cervical cancer is prevented by finding and treating abnormal cells before they develop into cancer.

Types of smear tests available

There are two types of tests:

• Conventional pap smear -  The smear taker smears cervical cells on to a glass slide.  At the laboratory, cells are stained and looked at under the microscope
• Liquid-based cytology - The smear taker places cervical cells into a liquid solution.  The laboratory then uses a machine to produce a layer of cells on a glass slide.  The cells are stained and examined under the microscope in the same way as the conventional smear test. 

Questions and answers on liquid-based cytology (LBC)

A copy of questions and answers on LBC can be downloaded here. Questions and answers on LBC (September 2009)

How effective is a smear test?

The cervical smear test is a screening test, not a diagnostic test.  That means the screening test is used to identify people who may not have an abnormality from those who may have, or may develop, an abnormality.

Cervical smear tests are a very good tool, but they are not perfect. In up to 20 percent of cases, abnormal cell changes can be missed and a result is reported as normal. This is called a false negative which can happen because:

• abnormal cells were hidden by blood or mucus so they could not be seen under the microscope
• cells with very slight changes were hard to interpret as normal or abnormal
• abnormal cells on the slide were missed by the person reading the smear
• very occasionally cancer may have already developed
• the cervical smear did not contain any abnormal cells, even though some were present on the cervix.

Regular smears are important, as these abnormal cells will usually be found in three years time when the woman has another smear. As cervical cancer usually takes many years to develop, the abnormal cells can still be treated to stop them from becoming cancer.

In up to 5 percent of cases, a result says a woman has some abnormal cells when she doesn’t. This is called a false positive. If a woman has been told her smear is abnormal, she will have a further smear or be referred for colposcopy.  The results from these will show there are no abnormal cells and no treatment will be needed.