How to think about medical screening tests: benefits, risks, and limits
Medical screening tests and procedures are popular and attractive to many people in the general population. Although useful in many instances, such as certain cancer screening tests that are recommended based upon age and family history, not all medical screening tests are always needed. And contrary to our general intuition, in clinical medicine, more information might not always be better for our health.
Let’s start by defining what a medical screening test means in this article. We define a medical screening test as one that is undertaken by someone who is feeling well (i.e., they do not have any symptoms) and who does not have certain specific diagnoses that might predispose them to other medical conditions (someone who would be termed as being at average risk of developing a particular condition). On the other hand, patients with actual symptoms or a known diagnosis or family history that confers additional risk might, in fact, require extra medical screening tests, and this article would not apply to them.
Examples of medical screening tests include cancer screening, blood-pressure screening, cardiac stress tests, “full-body scans,” batteries of laboratory tests, continuous vital sign monitors and others. Some of these medical screening tests have excellent supporting scientific evidence, while others do not. We would like to emphasize this distinction. Certain types of general medical screening for asymptomatic patients have been proven to be very useful for the population as a whole. However, many screening tests and procedures that are sometimes advertised are, in fact, not recommended for healthy patients at average risk—for good reason, as we will explain later.
There are many obvious potential benefits of medical screening tests. The main benefit is for a person to find out about a medical condition earlier than they would have otherwise known about it. However, the assumption that many people have is that early knowledge about a problem can allow us to intervene ahead of time and avoid the problem becoming more serious later. However, this may or may not be true, depending on the condition. There is an additional potential benefit of medical screening tests, which is appealing to some people but not everyone—the idea of simply knowing that a disease is present even though no intervention or cure is available. Importantly, though, for many people, such knowledge could create more anxiety rather than provide comfort. It is important to think about our own goals prior to screening for certain diseases if the answer is not truly desired in the end.
What is less obvious about unproven medical screening tests in the general population are the potential harms or risks associated with such tests. However, such potential harms and risks do exist and are often discussed more in the medical community than in the general population.
Let’s start with a potential risk that is often perceived as important to healthcare economists, epidemiologists or others who think about broad populations. That is the concept of excessive costs associated with screening tests which have not yet been proven to yield a significant net benefit for the population more broadly. It is of course true that as medical professionals, we all have a responsibility to think about the burgeoning costs of modern healthcare. However, for many individual patients, this argument might be unconvincing. Many people do not believe, understandably, that a price can be put on the detection of a serious condition that would help them with their health. Therefore, explaining other potential harms and risks might be more persuasive for some patients in demonstrating possible downsides of medical screening tests.
A major potential harm of unproven medical screening tests is the detection of false-positive results or a result that cannot be interpreted. For example, suppose an entirely asymptomatic and healthy person undergoes a blood test as part of a battery of tests that shows their C-reactive protein (a nonspecific marker of inflammation) is slightly above normal. What is the clinical meaning of this finding in a patient who is feeling completely well and has no other known medical problems? No physician would really be able to answer that confidently and correctly because there is no strong medical evidence to provide an answer, at least at present.
The downstream effects of false-positive medical screening test results can include at least two issues. First, the patient may unnecessarily feel a substantial amount of anxiety. This is not an insignificant issue. Worrying about the possibility of a serious medical problem can be extremely troublesome and disruptive to one’s life. When there is no strong evidence that the abnormality detected is clinically meaningful, this harm potentially outweighs the benefit of finding the abnormality.
Second, a more direct negative impact of identifying false-positive test results is that these abnormal test findings could result in additional diagnostic testing. Such diagnostic testing could yield additional false-positive test results, and the testing itself, if more invasive, could pose its own risks. All of these downstream actions would never have occurred if the initial false-positive result had not been identified.
Another potential risk of medical screening tests is false-negative test results. A false-negative test result is one where the test result is negative, but this result is actually incorrect. Another variation of this is a negative test result for a test obtained before a particular condition develops. A negative finding might provide false reassurance to the patient, who may be disappointed, angry, or confused if a serious condition were to be diagnosed after the negative medical screening test. An example of this is when patients who smoke tobacco products or have uncontrolled diabetes mellitus request cardiac stress tests to screen for significant heart-artery blockages even when feeling entirely asymptomatic. No current cardiac screening test can alter such a patient’s significantly elevated lifetime risk of developing heart-artery blockages. Yet, some patients might walk away feeling falsely optimistic after receiving their negative stress-test result.
In sum, medical screening tests are tests performed on patients who are feeling well and are at average risk for developing a particular medical condition. Some of these tests, such as (but not limited to) blood-pressure screening at recommended periodic intervals and testing for the presence of elevated cholesterol after a particular age, are highly recommended and supported by the best available medical evidence. However, not all medical screening tests have such supporting evidence. Excessive and unnecessary screening has many potential downsides, as described above.
Importantly, the burden of proof for using a particular medical screening test should be on those entities that promote their use. Of course, we should be open to the possibility that new medical screening tests in the future could provide valuable benefits to our patients. However, as new tests and technologies are debuted, it should be demonstrated that the net benefits of such new tests clearly outweigh the net harms. And consumers in the healthcare market should ask for this type of information and supporting evidence when evaluating their options.
By Prathit A. Kulkarni, M.D., assistant professor of Medicine at Baylor College of Medicine and Rohan R. Wagle, M.D., cardiologist and volunteer faculty member at Baylor College of Medicine
