Cervical smear test Dr Trisha Macnair It's estimated that screening for cervical cancer using the smear test saves up to 6,000 lives a year in the UK. But what does it involve and what can it tell you?

In this article

The programme What does it involve? Liquid-based cytology

The results Abnormalities

Problems with the test HPV and vaccines

All women between the ages of 25 and 65 are regularly invited for a smear test

Under the NHS Cervical Screening Programme, all women between the ages of 25 and 65 are regularly invited for a smear test. The system is automated, so as long as you're registered with a GP you should receive a letter asking you to make an appointment.

As a result of research that evaluated the optimal frequency for cervical screening, women are now invited for their first test at 25. They're then invited every three years until the age of 49, and every five years from 50 to 64.

From 65, only those who've had recent abnormal tests are offered another test.

During a smear test, some cells are taken from the cervix. These are sent to a laboratory for examination under a microscope. To be able to judge the cells properly, this is best done in the middle of your menstrual cycle, halfway between one period and the next.

The doctor or nurse will insert an instrument called a speculum into the vagina to allow them to see the cervix. A spatula is then wiped or scraped over the surface of the cervix to remove some cells, which are then transferred to a glass slide. The doctor or nurse may also do an internal examination to check for any problems.

The procedure can be uncomfortable but shouldn't be painful. Try to relax. Talk to the doctor or nurse if you're worried.

A new test called liquid-based cytology (LBC) is being introduced. This involves collecting the cells from the cervix using a plastic brush rather than a spatula. The cells are then put in a small vial of liquid and sent to the lab.

This allows the laboratory staff to get a clearer look at the cells, reducing the rate of inadequate smears from about nine per cent to just one to two per cent, so fewer women need a repeat test.

Results in numbers

For every 100 women who have a cervical smear test, around ten will be recalled for a repeat test because the first test didn't provide enough cells for study. Of those tests that are adequate for diagnosis, nine out of ten are normal.

Of the abnormal results:

• One in 20 will show borderline changes or mild changes (CIN1). These may go back to normal without treatment and most women simply need a repeat smear in six months.
• One in 100 will show moderate cell changes (CIN2). These women should be offered a colposcopy.
• One in 200 will show severe changes (CIN3). These women should be offered a colposcopy.
• Fewer than one in 1,000 tests will show invasive cancer. These women need immediate referral to a specialist.

You should receive the result of your smear test in writing within six weeks. The result will be either normal (negative) or abnormal. A small proportion of tests can't be completed because of a lack of visible cells on the slide. In such cases, you'll be invited for a repeat test.

An abnormal test doesn't necessarily mean cancer has been found or that it's likely to develop. The laboratory has simply identified some changes in the cells that require further investigation.

In many cases, these are just minor abnormalities that would disappear without treatment. However, a few will progress to cancer, which is why further investigation is warranted.

Abnormal cells are scaled from borderline normal ('not quite right') through mildly abnormal, severely abnormal to invasive cancer. Depending upon the degree of abnormality, women may be asked to have a repeat smear in six or 12 months or referred for a further test of the cervix known as a colposcopy.

A variety of terms are used to describe precancerous, or pre-invasive, abnormalities. The most widely used system is cervical intra-epithelial neoplasia, or CIN, which is divided into grades 1 (mild), 2 (moderate) and 3 (severe). These grades are related to the risk of the changes developing into cancer.

Studies have shown that if women with CIN3 aren't given adequate treatment, 36 per cent will have developed an invasive tumour 20 years later. But even though women with CIN1 have 47 times the normal risk of developing cervical cancer, in 50 per cent of cases the cells revert to normal if left alone.

The British Society for Colposcopy and Cervical Pathology has more information about invasive disease.

Screening is one of the best defences against cervical cancer

Screening is one of the best defences against cervical cancer and can prevent about 75 per cent of cancer cases in women who attend regularly. Put another way, for women aged between 25 and 39 undergoing smears every three years, a single negative result means a 41 per cent reduction in the chances of developing cervical cancer.

However, that doesn't mean the test is without problems.

Cervical screening isn't perfect. It can be difficult to tell an abnormal cell from a normal one, especially in the early stages of precancerous changes. In some cases that are reported as normal, abnormal cells are in fact present (a 'false negative' result). This occurs in between two and 20 per cent of tests, depending on the technique. However, more reliable tests are being developed.

Some tests are read as showing an abnormality when no disease is present (a 'false positive' result), which can lead to women undergoing unnecessary intensive treatment. However, it's difficult to know exactly how many false positives occur because treatment usually destroys the cells in question.

Perhaps the biggest problem is that those most at risk of cervical cancer slip through the net. Almost 80 per cent of eligible women attend their screening appointments, but almost half of new cases of cervical cancer in the UK occur in those women who've never had a smear test. In fact, the biggest risk factor for the disease is non-attendance for screening. The most important thing you can do to avoid cervical cancer is make sure you're registered with a GP and attend the screening offered to you.

Although it's not clear what causes abnormalities in the cervix to become cancerous, it is known that the human papilloma virus (HPV) plays an important role.

There are many types of HPV. Some are well known for causing genital warts, although these don't lead to cervical cancer. Others have been shown to cause abnormalities in the cells lining the cervix. These 'high-risk' types have been found in nearly every case of cancer of the cervix. Research has also shown that women with a mildly abnormal smear result who don't have a high-risk type of HPV infection are unlikely to develop cervical cancer.

Summary of advice

• Attend regular screening appointments. Failure to do so is the biggest risk factor in cervical cancer.
• The recall system is computerised, so make sure you're registered with a GP and that they have your correct name and address.
• If you don't receive the results of a test in writing, ask your doctor or call your local health authority (the number should be on your invitation letter).
• If you're concerned about your risk of developing cervical cancer, contact your GP or call NHS Direct on 0845 4647.

Testing for HPV as part of the screening programme may be a good way to spot those at high risk (but again, not actually diagnose cancer). However, at present more information on the value of HPV testing to the screening programme is needed.

A vaccine against many common strains of HPV has been licensed in the UK, and the Department of Health has recently agreed in principle to add it to the immunisation schedule for girls ages 12-13, subject to cost-benfit analysis.

It's likely this vaccine against cervical cancer will be introduced in autumn 2008 and should prevent at least 70 per cent of cases (it won't cover all types of HPV linked to cervical cancer). It's not clear if the vaccine will be offered to older girls and women. If your daughter is already sexually active and therefore at risk of HPV, you may want to talk to your GP about paying privately for this vaccine.

Further information on HPV is available from the NHS Cancer Screening Programme.

This article was last medically reviewed by Dr Trisha Macnair in August 2007.