Cervical screening test

Screening programme

Under the NHS Cervical Screening Programme, all women between the ages of 25 and 64 are regularly invited for a test to screen for cervical cancer every 3 to 5 years. 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 looked at 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 have not been screened since the age of 50, or who have had recent abnormal tests are offered another test.

What a screening test involves

During a cervical cancer screening 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 technique used is known as Liquid Based Cytology or LBC. This has now completely replaced the more old fashioned and less accurate smear test, and while people often casually refer to the test as a smear, you will no longer see it called this on official documents.

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. Then the end of the spatula, covered in cells, is broken off into a small vial of preservative liquid and sent to the laboratory. 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.

In the laboratory, cells from the fluid vial are examined under the microscope to check for abnormalities.

Results of cervical screening tests

You should receive the result of your screening test in writing within six weeks, although 98% of women now receive their result within 2 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. 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.

Results from the UK screening programme during 2010 - 2011 show that for every 100 women who had a cervical screening test, around 2-3 were recalled for a repeat test because the first test didn't provide enough cells for study. Of those tests that were good enough to check, more than 93% were negative for cancer cells - i.e. normal.

So 6% to 7% of tests show abnormalities. These changes vary from mild to more severe. The milder stages used to be described using a term called cervical intraepithelial neoplasia (as CIN1, CIN2 and CIN3), meaning cancer limited to the surface layer of the cervix. However, its now understood that the majority of these cases reverse back to normal or never progress to cancer, so the term is falling from favour. Instead of calling the changes "neoplasia" or cancer, the technical term "dyskaryosis" is used, meaning changes in the nucleus or control centre of the cell.

A break down of the 6-7% of abnormal tests shows:

• 3.5% of overall tests show borderline changes and 1.9% mild dyskaryosis (which used to be graded as CIN1). These may go back to normal without treatment and most women simply need a repeat test in six months
• " 0.5% show moderate dyskaryosis (CIN2)
• " 0.6% show severe dyskaryosis (CIN3)
• " Fewer than one in 1,000 tests will show outright invasive cancer

Depending upon the degree of abnormality, women may be asked to have a repeat test in six or 12 months or they may be sent to the hospital for a further test of the cervix known as a colposcopy and a review by a specialist.

What 'abnormalities' may mean

Our understanding of the significance of mild changes in the cervix has changed in recent years. There used to be concern that any but the most minor borderline changes respresented a risk of progressing to cancer, and should be treated. But research has shown that with time, mild dyskaryosis (CIN1 changes) return to normal in 57% of cases. In a further 32% of mild dyskaryosis (CIN1) the abnormalities simply persist without progressing to cancer (and so instead of needing treatment, they can just be monitored). Only 11% (or about 1 in 10) will progress to severe dyskaryosis (CIN3) and need colposcopy and more urgent treatment. Finally, about 1% eventually progress to invasive cancer.

So overall, 89% of borderline abnormalities or mild dyskaryosis (CIN1) go nowhere further. For this reason, most women are simply advised to have regular screening tests to keep an eye on the situation.

Another development in recent years has been the recognition that a virus, Human Papilloma Virus, plays a large part in the development of cervical cancer. (For this reason all young women are now offered vaccination against HPV.) So women who are found to have mild changes on cervical screening may be at greater risk of progression to cancer if they also test positive for HPV. Therefore many centres now also carry out an HPV test on women with abnormal cervical screening tests. If HPV is found, more active steps such as referral for colposcopy may be done sooner, while if HPV is not found the woman may simply be reassured and recalled for regular repeat screening tests.

The NHS Cervical Screening Programme has more information

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

Problems with cervical screening tests

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 tests 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.

Conversely, 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 screening 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.

HPV and vaccines

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 screening test result who don't have a high-risk type of HPV infection are unlikely to develop cervical cancer.