Medical tests are usually done to find out what is causing certain symptoms. Screening tests are different: they are done in people without any symptoms. They aim to detect diseases at an early stage, before any symptoms become noticeable. In many cases that can, but does not always, have advantages.
Detecting a disease at an early stage is only a desirable goal if treatment is then more successful. In other words, early treatment has to benefit people’s health. But, as with any medical intervention, tests sometimes do not have any benefits, or might even have harmful effects.
Some tests have more advantages than disadvantages, others do more harm than good, and some are still a subject of controversy. So it is worth weighing up the pros and cons of a test before deciding whether or not to have it.
Criteria for assessing screening tests
The World Health Organization (WHO) has defined criteria for evaluating tests, which may help you decide whether or not to have a particular test. The WHO criteria include the following:
Screening should be done only for diseases with serious consequences, so that tests have clear benefits to people’s health.
The test must be reliable enough, and not harmful in itself.
There has to be an effective treatment that works better when started at an early stage – in other words, before symptoms arise and you would have gone to the doctor anyway.
Neutral information should be made available to the public, so people can weigh up the pros and cons for themselves.
Most screening tests cannot prevent diseases
The aim of is to detect diseases before symptoms arise. Some tests also look for abnormal changes that could later develop into a disease. If found, abnormal changes are treated. But the test does not influence whether or not a disease develops or any abnormal changes occur.
Abnormal changes do not always develop into a disease
A lot of people have treatment as a result of tests, although they would never have gotten the disease. This is because many abnormal changes do not necessarily develop into a more serious condition, or might even go back to normal again by themselves, without causing any health problems.
No medical test is perfect
The medical tests that are used for often do not deliver a definite . They often just look to see if anything is abnormal, and then further tests have to be done to find out more.
In a lot of cases the abnormal test results turn out to be a false alarm. This can make people worry for no reason, and means that they sometimes have further tests that would not have been necessary.
Sometimes a test does not detect anything abnormal in people who are actually ill. In other words, it fails to detect a disease. Or the results might not be clear; they sometimes lie in a gray area between normal and abnormal results.
Screening does not offer any guarantees
If you have worrying symptoms, it is important to take them seriously and have them checked out by a doctor – even if the results of your last test were okay.
Questions to ask your doctor
If you are finding it hard to decide whether or not to have a test, it might help to talk to a doctor. Here are a few questions you could ask:
How likely am I to get this disease at my age?
Would detecting the disease early benefit my health in the long term? For instance, is there any scientific proof that it might help me live longer?
What adverse effects might be associated with the test, with possible tests following , and with the treatment? How common are they?
How often, and at what intervals, will I have to have a test in order to be able to benefit from ?
How often does the test lead to false alarms, and how often does it fail to detect a disease?
Do not worry too much about things that might never happen
A wide range of tests are available nowadays. Some are considered to be worthwhile. Others have not yet been well researched or do not have an overall benefit, but are still offered and sometimes even strongly promoted. That might give people the impression that there are diseases lurking around every corner, and that you can protect yourself from them.
But in most cases the risk of getting one of the diseases that can be screened for is not particularly high. And even the best tests cannot guarantee your health. We all have to live with the fact that we might get ill. So it is best not to worry too much or drive yourself crazy thinking about diseases that you do not have, and probably never will.
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IQWiG health information is written with the aim of helping people understand the advantages and disadvantages of the main treatment options and health care services.
Because IQWiG is a German institute, some of the information provided here is specific to the German health care system. The suitability of any of the described options in an individual case can be determined by talking to a doctor. informedhealth.org can provide support for talks with doctors and other medical professionals, but cannot replace them. We do not offer individual consultations.
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