Screening tests check to see if you have a disease or condition before you have any symptoms of it. The idea is that a problem is picked up before it develops, or in the very early stages. In this way, certain diseases can be prevented before they ever occur, or treated before they start causing any problems.
Not all conditions have suitable tests which allow them to be detected early, and not all conditions can be treated successfully even if they are picked up. So only certain conditions are part of our national screening programmes. The screening programmes currently available in the UK are listed below.
What are screening tests?
A screening test is a check done on a healthy person to pick up a condition before it develops, or at a very early stage. If the screening test is positive, further tests are needed. If these further tests confirm the result, treatment may be needed.
For example, there is a long pre-cancer stage in most women who develop cancer of the neck of the womb (cervix). At this stage, there is a treatment which can stop abnormal cells developing into cancer. So, if detected by the cervical screening programme, the woman can be treated and will never develop cancer of the cervix.
Other conditions are detected while still in the early stages whilst they are easier to treat and before complications develop. This is the case in the Abdominal Aortic Aneurysm Screening Programme. An aortic aneurysm is a swelling in the main blood vessel (artery) of the body. Where the wall of the artery is swollen, it is weakened. As it gets bigger, it gets weaker and then may burst (rupture). Because it is such a big artery, once it bursts, a lot of blood is lost very quickly and many people do not survive. However, if picked up early, the artery can be repaired in a routine operation which is much less risky. Some cancers (such as breast cancer and bowel cancer) may also be picked up in the early stages. If treated early, they are less likely to spread.
The type of test done is different for different conditions. For example, the screening test for an aortic aneurysm mentioned above is an ultrasound scan. The screening test for breast cancer is a special X-ray called a mammogram. The screening test for cancer of the cervix is a cervical smear. Some screening tests are blood tests. Some screening tests involve a physical examination. Each screening programme has its own website (see the links in the last section below) which explains which test is done and what this involves.
What conditions are suitable for screening tests?
A large number of criteria must apply before a national screening programme is considered. For example:
- There must be a test available which picks up a disease or condition before symptoms develop.
- This test must be reasonably accurate. It should not be positive for too many people who do NOT have the condition and it must not miss many people who DO have the condition.
- The test must be reasonably simple to perform and acceptable to the people having the test.
- The benefits of the screening test must be greater than any potential harm or risks it could cause.
- The cost of the test, once done nationally for lots of people, must not be more than the benefits it gives.
- There must be a treatment at the early stage of the condition or disease which will make a difference to the outcome. There is no point in screening for something if doctors are unable to do anything about it.
- The condition being screened for must be important to health and well-being.
- There must be an organised, efficient plan for what happens if the test is positive.
These are just some of the things which have to apply before a screening programme is rolled out across a country. In many conditions there is not a suitably precise test, or there is not enough evidence that early treatment makes a difference. For example, there is not yet a national screening programme for prostate cancer. There is a blood test, called the Prostate Specific Antigen (PSA) test. However, experts do not feel it is accurate enough. Many men who do not have prostate cancer would have to have further investigations, which may themselves cause harm. Also it is thought that not all early prostate cancer develops into a spreading cancer which causes a problem. So some men might have unnecessary treatment for something which was never going to harm them. Not all experts agree but currently it is thought screening all men would cause more harm than benefit. Therefore, this screening test is only used where doctors feel it would be helpful, or for men who choose to have it having understood the pros and cons. It is not a national screening programme.
What are the benefits of screening tests?
Screening tests which have become part of the UK screening programme are believed to have great benefits. In picking up problems early, many lives are saved and many health problems prevented. It is thought, for example, that 4,500 lives are saved every year in the UK by cervical screening. For other cancers which are picked up in the early stages, treatment is more likely to be successful. Operations involved are less extensive in the early stages of a cancer than in later stages. There is less chance of the cancer spreading if it has been detected early.
A number of screening programmes exist for newborn babies. These pick up uncommon abnormalities, which may be corrected if picked up early enough. For example, newborn babies have a thorough screening examination after birth, which is repeated at six weeks. This is to look for certain problems with their eyes, heart, testicles and hips. This prevents health issues later on in life, such as loss of vision, arthritis of the hips and infertility.
Other screening programmes involve tests for pregnant women. One such test is a scan to look for serious abnormalities in the baby. Women may choose to have the test or not. If a woman has the test and it is positive, she and her partner may choose not to continue the pregnancy if the abnormalities are very serious.
To see the benefits of each individual screening programme, see the links below where the tests are listed.
What are the problems with screening tests?
All the advantages of screening tests have to be weighed against the possible problems or harm which they might cause. Issues to consider include:
- No test can be absolutely guaranteed to be accurate. So some people may be falsely reassured; others may think they have a problem which they do not.
- Some people may have treatment which wasn't actually needed as a result of a positive test.
- Tests can cause a lot of worry. This is particularly the case if a screening test comes up positive but further investigations are normal.
- Cost. Screening large numbers of healthy people is expensive and uses funds which could otherwise be used to treat ill people. (Where the balance is right, this cost will be balanced by preventing health issues which are expensive to treat in future, however.)
- For some conditions screened, a negative result at one point in time does not rule out developing the condition in the future. The test cannot guarantee any protection for the years to come.
As discussed above, many illnesses do not have a test which fits all the conditions needed to use in a screening programme. There are many conditions which it would be better to pick up early but for which there is no suitable test.
Even in well-established screening tests, such as breast screening, experts differ in their opinion about whether the benefits are worth the harms.
What screening tests are available in the UK?
Currently the following screening programmes are running in the UK:
- , which includes:
- Newborn Hearing Screening.
- Newborn Bloodspot Screening.
- and , which include:
- Newborn Physical Examination Screening.
- , which includes:
- Fetal Anomaly.
- Infectious Diseases in Pregnancy.
- Sickle Cell and Thalassaemia.
Further reading and references
; Public Health England, February 2013
; NHS Health Scotland
; Public Health Wales
; Public Health Agency Northern Ireland