March 2017

To Screen or Not to Screen?
The Benefits and Harms of Screening Tests

Illustration of a doctor holding a vial of blood while talking with a patient.

Catching chronic health conditions early—even before you have symptoms—seems like a great idea. That’s what screening tests are designed to do. Some screenings can reduce your risk of dying from the disease. But sometimes, experts say, a test may cause more harm than good. Before you get a test, talk with your doctor about the possible benefits and harms to help you decide what’s best for your health.

Screening tests are given to people who seem healthy to try to find unnoticed problems. They’re done before you have any signs or symptoms of the disease. They come in many forms. Your doctor might take your health history and perform a physical exam to look for signs of health or disease. They can also include lab tests of blood, tissue, or urine samples or imaging procedures that look inside your body.

“I wouldn’t say that all people should just simply get screening tests,” says Dr. Barnett S. Kramer, a cancer prevention expert at NIH. “Patients should be aware of both the potential benefits and the harms when they’re choosing what screening tests to have and how often.”

Teams of experts regularly look at all the evidence about the balance of benefits and harms of different screening tests. They develop guidelines for who should be screened and how often.

Choosing whether you should be screened for a health condition isn’t always easy. Screening suggestions are often based on your age, family health history, and other factors. You might be screened for many conditions, including diabetes, sexually transmitted infections, heart disease, osteoporosis, obesity, depression, pregnancy issues, and cancers.

Every screening test comes with its own risks. Some procedures can cause problems like bleeding or infection. A positive screening test can lead to further tests that come with their own risks.

“Most people who feel healthy are healthy,” says Kramer. “So a negative test to confirm that you’re healthy doesn’t add much new information.” But mistakenly being told that you do or don’t have a disease can be harmful. It’s called a misdiagnosis.

A false negative means that you’re told you don’t have the disease, but you do. This can cause problems if you don’t pay attention to symptoms that appear later on because you think you don’t have the disease. A false positive means that you’re told you may have the disease, but you don’t. This can lead to unnecessary worry and potentially harmful tests and treatments that you don’t need.

Even correctly finding a disease may not improve your health or help you live longer. You may learn you have an untreatable disease long before you would have. Or find a disease that never would have caused a problem. This is called overdiagnosis. Some cancers, for example, never cause symptoms or become life-threatening. But if found by a screening test, it’s likely to be treated. Cancer treatments can have harsh and long-lasting side effects. There’s no way to know if the treatment will help you live longer.

An effective screening test may decrease your chances of dying of the condition. Most have not been shown to lengthen your overall life expectancy, Kramer explains. Their usefulness varies and may depend on your risk factors, age, or treatment options.

If you’re at risk for certain health conditions—because of a family history or lifestyle exposures, like smoking—you may choose to have screenings more regularly. If you’re considering a screening, talk with your health care provider. 

 

 

References
Population-based screening for cancer: Hope and hype. Shieh Y, Eklund M, Sawaya GF, et al. Nat Rev Clin Oncol. 2016 Sep;13(9):550-65. doi: 10.1038/nrclinonc.2016.50. Review. PMID: 27071351.

 

NIH News in Health, March 2017