Accuracy of cervical screening results
Cervical screening is one of the best ways to protect yourself from cervical cancer.
Since CervicalCheck started in 2008:
- more than 3 million screening tests have been done
- the number of people who develop cervical cancer has fallen
- over 100,000 cases of abnormal cervical cells have been found and treated - many of these could have developed into cancer if not found through screening
But screening does not prevent all cases of cervical cancer.
You can test negative for types of human papillomavirus (HPV) and still develop cervical cancer. HPV is the main cause of cervical cancer.
Abnormal cells in the cervix can also be missed.
If 1,000 people are screened, about 20 people will have abnormal (pre-cancerous) cervical cells:
- 18 of these 20 people will have these cells found through screening
- 2 of these 20 people will not have these cells found through screening and may develop cervical cancer
This is why we invite you at regular intervals for a screening test.
Inaccurate test results
Sometimes test results are inaccurate. We call these results 'false positives' and 'false negatives'.
False positives and false negatives are unavoidable. They happen in every screening programme.
But the introduction of HPV cervical screening will mean fewer false negatives than before. This is because it is a better way to screen for cervical cancer.
False positive results
A result may be reported as positive even though there is no HPV infection or changes to cells of the cervix. This is called a 'false positive'.
A false positive may mean you will have further tests that ultimately confirm there was no risk of cancer at that time.
False negative results
A result may be reported as negative even though there is a HPV infection or abnormal cells in the cervix. This is called a 'false negative'
A false negative may mean that you will not have been sent for further tests when there may have been a chance to stop cancer developing.
Because of this, it's important that you:
- always pay attention to possible symptoms of cervical cancer
- attend your screening tests when they are due
If you have concerns or symptoms, talk to your GP immediately. Even if you have had a recent normal screening result, never ignore symptoms.
Why abnormalities can be missed
Your sample will be checked for HPV first. If HPV is found, it will also be checked for abnormal cells.
But not everyone who develops cervical cancer will have HPV found at screening.
A negative HPV test also does not mean you won't get the infection in the future.
Abnormal cells can also be missed.
This is because:
- sometimes abnormal cells do not look much different to normal cells
- there may be very few abnormal cells in the sample
- the person reading your sample may miss the abnormality (this happens occasionally, no matter how experienced the reader is)
No test in any screening programme will find every woman who has abnormal cervical cells.
Cervical cancer takes many years to develop. In most cases, it takes 10 to 15 years for cells to go from normal to abnormal to cancer.
If your sample was positive for HPV, you will have a repeat test in 12 months.
This means that if abnormal cells were missed on one screening test, they should be found quickly on the next test.
This is why you should always attend your cervical screening test when it's due.