Introduction

Reviews

Deciding Whether You Need to Have a Test

Timothy B. McCall, M.D.

Here are some rules of thumb when evaluating the risk and benefits of a proposed test:

• The test shouldn’t be worse than the disease. Any invasive test can cause a side effect. Liver biopsies occasionally lead to fatal hemorrhages. X-ray studies of the kidney can precipitate kidney failure. I once treated an elderly man who nearly died when he went into anaphylactic shock (the most serious type of allergic reaction) after being injected with contrast dye for a CAT scan of his head. His doctor had ordered the test because the man was depressed, which experts consider an insufficient reason to order a CAT scan—particularly one with contrast dye. Luckily, shots of adrenaline and other medicines raised his dangerously low blood pressure and saved his life
• It’s not always better “to do the tests and to know.” At times, it may be preferable to tolerate a remote chance that something will go undiagnosed, than to risk a serious side effect of a test. If there’s a one in 1000 chance you’ve got cancer and the test to diagnose it kills one in 500, the odds favor not doing the test.
• Even tests with potentially serious side effects are advisable if the risks are outweighed by the benefits. If there’s a one in ten chance you’ve got a curable cancer and the test to diagnose it kills one in 500, it a risk well worth taking. Although a CAT scan of the head is considered inappropriate for someone whose only symptom is depression, if other symptoms pointed to the possibility of a brain tumor, the test would be advisable.
• Think like a chess player. Good chess players anticipate the next several moves, before making a decision. When evaluating the risks and the benefits of a test, consider what you would do if the test came back abnormal. Ask the doctor what he or she would likely recommend. Then try to anticipate how you’d feel. If the test were abnormal, would you proceed to have a more-invasive test or an operation if recommended? If you’re certain you’d refuse to take the next step, it sometimes makes sense to avoid the first one.
• Your values matter the most. Different people will look at the same information on the risks and benefits of a test and will come to opposite conclusions. Individuals differ in the value they place on resolving uncertainty and on tolerating risk—both of testing and of not testing.

Here's an example to show what I mean: Say a healthy 35 year old man notices a little blood on the toilet paper while wiping himself after a bowel movement. Recognizing this as a warning sign of colon cancer, he visits his doctor. The doctor discovers a hemorrhoid and is reasonably certain it’s the cause of the bleeding. The doctor tells him colon cancer is rare in a healthy man his age without a family history of colon problems but does occur.

To know for sure that he doesn’t have colon cancer, the man would have to undergo a test or a series of tests, that are uncomfortable, expensive and, while generally safe, not without risk. If he doesn’t have the tests, he will have to accept the remote chance, say one in 10,000, that he has an undiagnosed cancer. In this circumstance, some people would say If there’s a one in 10,000 risk of cancer, I want the tests. Others would say You’re not doing those tests to me. I’ll take my chances. The point is that the decision is a value judgment. There is no right answer.

For a 65 year old man in the same situation, almost all doctors would recommend the tests, since colon cancer is common at that age. If the man were 25, few doctors would recommend the tests, since the chance of cancer is remote. The proper course of action is clear at the extremes of age but there is a substantial gray area. Different doctors will draw the line at different points. Remember, though, a doctor’s recommendation that you have a test may be colored by many factors including concern over a potential malpractice suit. The question should not be How much uncertainty is your doctor willing to accept? but rather How much uncertainty are you willing to accept?

Next: Go Where the Money Is

Return to Examining Your Doctor