Cervical Smear Test
What does it involve?
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 wooden 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 it shouldn’t be painful. Try to relax. Talk to the doctor or nurse if you’re worried.
Liquid based cytology
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.
You should receive the result of your smear test in writing within six weeks. The result will be either normal (ie, negative) or abnormal. (A small proportion of tests are unable to 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 is 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 may be referred for a further test of the cervix known as a colposcopy.
A variety of terms are used to describe pre-cancerous, 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.
Screening is one of the best defences against cervical cancer and can prevent around 75 per cent of cancer cases in women who attend regularly. 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 pre-cancerous 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 occur in those women who’ve never had a smear test. In fact, the biggest risk factor for the disease is non-attendance of screening.
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.
Testing for HPV as part of the screening programme may therefore 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. Several trials are underway, the results of which will hopefully improve our understanding of HPV.
This article was last medically reviewed by Dr Trisha Macnair in August 2005.
First published in November 1997.
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- Attend regular screening appointments. Failing to do so is the biggest risk factor in cervical cancer.
- The recall system is computerised, so make sure you are 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.