Five Facts of Medical Screening

Alan Cassels, author of Seeking Sickness, reveals shocking facts about medical screening, and questions essential to ask before facing the process.

1. Most screening tests have insufficient evidence to prove that they work: that is, to find disease before it develops into a form that could hurt you, early enough so that doctors can do something acceptable to save your life.

This includes such procedures as screening for mental illness, whole body scans, and the very common and frequently ordered screening tests for high cholesterol.

2. Many screening tests are very good at finding disease, but they also find a lot of ‘pseudodisease’ along the way. Many people will get medical procedures - more scans, biopsies, drugs, and surgeries – for symptoms that would never have gone on to hurt them.

This includes mammography that finds calcifications in breasts that look like cancer but aren’t, and prostate-specific antigen tests that produce ‘high’ readings associated with a higher risk of a common type of prostate cancer (but which will never go on to hurt anyone).

3. Many screening tests are for ailments that are extremely rare even in ‘high risk’ people.

This includes screening for lung cancer. A seven-year screening program of 53,000 heavy smokers found that less than two percent of them would die of lung cancer but over 95 percent of them would find false positives - positive tests for cancers that turn out not to be cancers.

4. Many screening tests produce a lot of extra and unnecessary disease and sickness because of the procedures and biopsies done, on people whose lives were not saved. These people have been over diagnosed.

After screening 2,100 women for 11 years for breast cancer, one life will be saved, but that testing will cause nearly 700 false positives, which leads to follow-up testing (more x-rays and investigations) and 75 women having an unnecessary biopsy.

After screening 1,410 men for prostate cancer using a simple PSA test, 48 of those men will be treated (with chemotherapy, surgery or drugs) and of those treated, 30 will end up impotent or incontinent. All this testing will prevent one man from dying from prostate cancer.

5. Many proponents of screening have conflicts of interest, and stand to gain financially from the expansion of screening. These conflicts are often not revealed in the media or marketing of the screening test.

Conflicted people in the screening world include surgeons, owners of testing equipment, radiologists, patient disease advocates, and pharmaceutical manufacturers.

Questions to ask when facing a screening test:

• Will the test save my life? Can it find something early enough so that the doctors can do something to prevent the disease from ultimately killing me?
• Is there a ‘cure’ for the disease that they find? In other words, can they actually do something to save my life from this disease they are seeking, or do something to otherwise improve my odds?
• How accurate is the test? What is the rate that it delivers false positives - findings that aren’t disease - or false negatives - findings that indicate no disease when it is actually there?
• What do independent sources (such as the US Preventative Services Taskforce) say about this test?
• Who stands to benefit (financially) from having me screened?
• What happens if I do nothing?