Don’t assume earlier detection of ‘disease’ is better.
Early detection of disease and ‘treating’ people who have an increased risk of disease can sometimes be beneficial, but this is not always the case. Early detection of disease sometimes causes harms, and early detection of a health problem is only helpful if an effective treatment is available and has been shown in fair comparisons to work better if it is started early.
Explanation
People often assume that detecting or diagnosing a health problem early leads to better outcomes, such as less chance of dying from cancer. Early detection of disease or of risk of disease, before the disease has become apparent, is called ‘screening’. Screening can be helpful but is sometimes harmful. Screening people to detect disease and starting treatment in people at increased risk of disease is only helpful if two conditions are met. First, there must be an effective treatment. Second, people who are treated before the disease becomes apparent must do better than people who are treated after the disease becomes apparent.
Screening and treating people at increased risk of a disease can harm people in several ways. Screening tests can be bothersome and may occasionally cause harm. Screening tests can be inaccurate. For example, they can indicate that people have a disease when in fact they do not, which can cause unnecessary worry and treatment. Screening can lead to the detection of a condition or problem that would never cause a person harm during their lifetime (overdiagnosis), which also can cause unnecessary worry and treatment. Screening can lead to people receiving more extensive or invasive treatment than is required to improve their health (overtreatment). For example, men with prostate cancer detected by screening can be treated with surgery and radiotherapy even though the cancer may not have caused them any harm in their lifetime. Screening or treating a risk factor for a disease as if it is a ‘disease’ can also cause harm by labelling people as being sick when they are not, and screening may result in the use of diagnostic tests and treatments that may cause harms.
Examples
Screening for phenylketonuria (PKU) is an example of early detection of disease that is better than late detection. PKU is a rare inherited illness. People with PKU cannot metabolise an amino acid called phenylalanine. If it is not treated early, PKU results in severe intellectual disability, epilepsy, and behavioural problems. PKU can be detected in newborn babies with a drop of blood. Treatment includes a special diet and regular blood tests. With early diagnosis and treatment, most children with PKU can live healthy lives.
Screening women without symptoms for ovarian cancer is an example of early detection that does more harm than good. In fair comparisons with nearly 300,000 women, there was not an important difference between women who were screened and those who were not screened in the number of women who died from ovarian cancer. The comparison also found harms of screening, including unnecessary surgery (with major surgical complications) in women found to not have cancer.
Remember: Early detection of a health problem or disease is not always better.
- Book: Early is not necessarily better. In: Testing Treatments.
- Book: Screening tests that detect disease early are not always beneficial. They can lead to people living more years with disease rather than longer lives. In: Smart Health Choices.
- Video: What is overdiagnosis? This is an informedhealth.org video lasting 3:34 minutes.
- Video: A Bridge Over Diagnosis. This is a parody by James McCormack lasting 5:12 minutes.
- Article: Screen test. The Guardian.
- Article: Misconceptions About Screening. BuzzFeed.
- Article: Making sense of screening. Sense about Science.
- Blog: Earlier is not necessarily better. Students 4 Best Evidence.