A screening test is a test that is supposed to detect a disease in the general population when it doesn’t cause any symptoms.

For it to be worthwhile to test the whole population, it needs to be a reasonably common disease. Otherwise, it makes finding a needle in a haystack look easy.

The test has to be relatively inexpensive, and not cause any risk to an otherwise healthy population.

It has to be sensitive enough that it can detect most people who have the disease.

And it has to be specific enough to be able to accurately find disease and not find harmless things that look like disease.

There needs to be a cure for the disease that is being diagnosed; if not, it doesn’t do the patient any good.

And it needs to be cost effective. If it is prohibitively expensive, it cannot be used routinely in the whole population.

Very few tests have fulfilled all these criteria.

Mammograms have fulfilled all these criteria, because Breast Cancer is a common disease, can be detected in a curable state and don’t in themselves cause harm. There has been controversy in the age at which screening begins, because the sensitivity (ability of the test to detect real disease) has been debated in the age group of 40-50 years. Some organizations think that mammograms detect disease more accurately after the age of 50, others think that they can detect it accurately enough after age 40.

Pap Smears have been proven to detect Cervical Cancer early, as well as pre cancer lesions, when they can be effectively eradicated by local treatments, which are minimally invasive. They need to be done annually throughout early adulthood through middle age. After that, they can be done every three years, if the woman has 3 normal tests and has only one steady sexual partner.

Colonoscopy detects early stage colon cancer, or polyps which might turn into cancer. In people not at high risk from bowel diseases or family history, screening begins after 50, and continues every 3, 5 or 10 years, depending on what is found. People are strangely reluctant to have this test, even women who have had breast cancer diagnosed by a mammogram and know the value of a screening test. It’s not a difficult test. A day and a half of cleansing, and sedation during the test, and you are done. It’s worth it.

PSA is a blood test for prostate cancer, that  has been used, but not well established in saving lives by using regularly in the general population. It is unclear that treating all prostate cancer at an early stage saves lives, i.e. causes less deaths directly from prostate cancer. On the other hand, all prostate cancer treatment causes side effects. That issue is still being hashed out. I have asked several leading Prostate Cancer experts who are men, whether they do a PSA on themselves, and the answer has been mostly “no”. We will come back to this issue in the future.

CA 125 is another blood test that is touted by women’s magazines to be THE screening test for ovarian cancer. It is not. It is falsely increased for any non cancer event going on in the abdomen; this leads to unnecessary anxiety and invasive procedures. It is a useful test to follow the course of diagnosed disease, not as a screening test.

Other tumor markers are useful to follow the course of the disease, once it is diagnosed. Not for initial diagnosis.

The newest finding that is being evaluated is the low dose CT scan of the chest, in the high risk population. We know that smokers get lung cancer at higher rates than non smokers. But how do we effectively screen and how often do we do the screen, to pick up lung cancers early enough to treat, without having to biopsy every shadow that shows up? And without subjecting the large population of smokers to unnecessary amounts of radiation from regular CT scans. A recent study has shown some survival benefit to a new technique of low dose CT scans, which are only used for screening.

There have been fads that prey on people’s vulnerability: whole body CT scans,  or other unproven screening procedures. So you get your whole body scan this year, and it didn’t show anything. Will you repeat it every year? For how long? How about the radiation exposure that it will accumulate? We do not recommend these.