Before You Screen: A Practical Guide to Choosing Tests That Help More Than They Harm

 

Screening can save lives in the right circumstances. But more tests, more often, do not automatically mean better health or a longer life. The most useful question is not, “What else can we test?” It is: “What is this test likely to change for someone like me?”

A screening test is performed when a person has no symptoms. That makes the decision ethically important: because you feel well, the test needs a strong likelihood of producing more benefit than harm. Some screening programs lower deaths from a particular disease in clearly defined higher-risk groups; others detect more abnormalities without convincingly extending overall lifespan. For example, a large review of long-term randomized trials found evidence of modest life extension for colorectal screening by sigmoidoscopy, while longevity benefits for several other common cancer-screening approaches were uncertain or not statistically demonstrated. 

This does not mean that screening is useless. It means that intelligent prevention is more valuable than reflexive testing.

Start with your individual risk

A test that is sensible for one person can be unnecessary—or even harmful—for another. Before agreeing to a screening test, consider the factors that change its likely value:

• Your age and sex.

• Family history of cancer, heart disease, genetic conditions, or early deaths.

• Smoking history, alcohol use, occupational exposures, and other lifestyle risks.

• Existing conditions, medications, and prior abnormal results.

• Your overall health and estimated ability to benefit from treatment if a serious condition were found.

• Whether you have symptoms—because a symptom needs diagnostic evaluation, not “routine screening.”

For example, low-dose CT screening for lung cancer is not a general test for everyone. Evidence of benefit comes from carefully selected people at substantial risk because of their smoking history; the NELSON trial reported a lower risk of lung-cancer death in its screened high-risk population. Applying the same test broadly to people at low risk can create more false alarms, incidental findings, radiation exposure, and invasive follow-up without the same likelihood of benefit. 

Ask what outcome the test improves

A common source of confusion is the difference between finding disease earlier and helping people live longer or better.

A screening program may appear successful because it finds more early-stage disease or because people diagnosed through screening seem to survive longer after diagnosis. But these numbers can mislead. If a cancer is found two years earlier while the date of death does not change, the person appears to have “survived longer with cancer” even though the outcome was unchanged. This is called lead-time bias. The older Mayo Lung Project illustrates the problem. Intensive screening found more lung cancers and appeared to improve survival after diagnosis, yet extended follow-up did not show a reduction in lung-cancer mortality in the intervention group. Researchers concluded that some lesions with limited clinical relevance may have been detected through screening. 

When discussing a test, ask your clinician:

1. Does this test reduce deaths from the disease—not merely find more cases?

2. Does it improve overall survival, quality of life, or prevent serious illness?

3. What is the absolute benefit for people with my risk profile?

4. How many people like me need this test for one person to benefit?

5. What happens if the result is abnormal?

Understand the possible harms

Screening is often presented as harmless reassurance. It is not always harmless.

• False positives: A concerning result may turn out not to be cancer or disease, but can still trigger anxiety, repeat imaging, biopsies, procedures, expense, and time.

• Overdiagnosis: Some abnormalities would never have caused symptoms or shortened life, yet once discovered they may lead to surgery, radiation, medication, and years of worry.

• False reassurance: A normal screening result does not mean that future symptoms should be ignored.

• Treatment harms: Detecting a condition early matters only if treatment provides more benefit than harm.

• Opportunity cost: Time, attention, and resources devoted to low-value testing may distract from interventions with clearer benefits, such as smoking cessation, blood-pressure control, vaccination, exercise, sleep, and treatment of existing illness.

The National Cancer Institute notes that screening can lead to unnecessary and invasive follow-up tests, anxiety from false-positive results, and other harms; it also emphasizes that detecting cancer earlier does not necessarily reduce cancer deaths. Use a “before the test” checklist

Before scheduling a screening test, pause and use this checklist:

• Why am I being offered this test now?

• Am I in the group studied in the trials that showed benefit?

• What is my personal chance of benefit?

• What are the risks of false positives, overdiagnosis, radiation, or invasive follow-up?

• If the result is positive, what tests or treatments would follow?

• Would I want—and be medically able—to undergo those next steps?

• What happens if I wait, decline, or repeat the test later?

• Is there a guideline from an independent medical body that supports this test for someone like me?

A good clinician should welcome these questions. The goal is not to demand certainty—medicine rarely offers it—but to make the decision consciously, rather than allowing habit, fear, advertising, or “just in case” thinking to decide for you.

Choose informed prevention

The responsible alternative to routine overtesting is not neglect. It is informed prevention.

Keep recommended screenings that have a favorable evidence-based balance for your particular risk group. Do not skip evaluation of new or persistent symptoms. Maintain regular clinical care, and focus seriously on preventive measures with broad benefits: avoiding tobacco, controlling blood pressure and diabetes, staying physically active, eating well, sleeping adequately, receiving appropriate vaccines, and addressing mental health.

Screening should be a conversation, not an automatic ritual. The best test is not necessarily the newest, most frequent, or most comprehensive one. It is the test that has a credible chance of helping you—before the machine is turned on.

This article is for education and should not replace individualized medical advice. Decisions about screening should be made with a qualified clinician who knows your medical history, risk factors, and current symptoms.

You can learn more by reading this article 

Mykola Iabluchanskyi together with Andriy Yabluchanskiy