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Is There Such a Thing as an Unnecessary Diagnostic Test?

As I was driving home from work this morning after a night shift I heard a story about the health care debate on the radio...

Dr. Eric Barchas  |  Oct 23rd 2009


As I was driving home from work this morning after a night shift I heard a story about the health care debate on the radio news. The topic was one of the most poorly understood concepts in the debate: unnecessary diagnostic testing.

Many people have cited the elimination of unnecessary tests as a way to reduce health care costs. As a medical clinician I would like to know how an unnecessary test is defined.

It is not possible to know whether a diagnostic test is necessary without knowing the results. In other words, it is not possible to know whether a diagnostic test is necessary without running it. Only with hindsight can one determine whether the test was needed.

Consider the following example from veterinary medicine. Imagine your dog has suffered a two day period of lethargy and poor appetite. You authorize your veterinarian to run basic blood tests. The results are normal, but the ratio of blood sodium and potassium levels is on the low end of what is considered normal.

In cases such as this, the overwhelming majority of dogs do not have a serious condition. Transient gastrointestinal upset due to dietary indiscretion is most likely. An adverse reaction to a mild toxin also may be to blame. A self-limiting viral infection or dozens of other mild pathologies could be the cause of the issue. All of these problems generally resolve on their own.

But a much more serious problem can cause the symptoms and initial test results I have described: Addison’s disease. Addison’s disease is much less common than the milder problems I have described above. But if it is not detected and treated it is deadly.

The test for Addison’s disease is specialized and expensive. It is non-invasive and low risk. Without the test, it is not possible to know whether the syndrome is causing the symptoms. The treatment for Addison’s disease can be harmful to dogs who don’t have the syndrome.

Imagine that one out of every thousand dogs with lethargy, poor appetite, and a borderline sodium to potassium ratio has Addison’s disease. If a thousand dogs develop the symptoms I have described (and initial test results are as I have described), 999 of them will get better without treatment. One will die.

Those may sound like good odds. But what if your dog is the one?

If you think a one-in-a-thousand chance isn’t bad, I hope you don’t buy lottery tickets. The odds of hitting the mega jackpot make one-in-a-thousand look almost certain.

When I treat dogs like the imaginary one in this post, I always recommend the test for Addison’s disease. After I get the results, I usually learn that the test was not necessary. But every once in a while the test saves a dog’s life. In those instances the test was very necessary indeed.