In my previous post, I talked about medical tests and how “normal” and “abnormal” results do not always correlate to healthy or sick. The bottom line from that discussion is that while tests are essential to diagnosing illness, they are fallible. Put another way, if you do enough testing on anyone, some tests are bound to turn up “abnormal” regardless of whether the person has a real abnormality. So, what does it mean when we have an abnormal test result?
The first step is to try to determine whether there is an actual abnormality causing the result or whether the test is a false positive. The easiest step to take is to repeat the test. Repeat testing is likely to make many “abnormalities” disappear. This is particularly true if the abnormal test is not correlated with any symptoms or signs indicating disease.
If the test is abnormal a second time, the best course of action is determined by at least four factors:
- the clinical situation
- what happens with the passage of time
- the risks of further testing
- the risks versus the benefits of treatment
Most situations involve interplay among these factors, so it is impossible to come up with one rule that dictates what to do. Here are some examples of how these factors come into play.
The Clinical Situation: Abnormal tests that correlate to symptoms or signs of disease are much more likely to be true positives. So a positive strep culture in a person with severe sore throat and fever is likely to indicate streptococcus infection. With a sore throat and a positive test a physicians wouldn’t want to repeat that test; they would just treat the patient with antibiotics.
In contrast, a slight abnormality when there is no corresponding problem might well be ignored or just followed. A patient of mine who had platelet count that was just below normal comes to mind. Platelets are blood elements essential for clotting, so a low platelet count raises concerns about bleeding. However, this person had no abnormal bleeding or any other abnormalities in his blood cells. Rather than embark on a bone marrow sampling, a painful procedure, we decided to just wait and repeat the test. Three months later, the platelet count was the same. In fact, over the next two years, the results didn’t change. This person’s normal was just a little lower than that of the general population. The test results were slightly low, but did not require clinical action at all. Clinical intervention would have been painful and potentially harmful.
What Happens With the Passage of Time? One of the most useful of clinical tools is “watchful waiting,” seeing what happens over time. Does the abnormality disappear or remain unchanged, or does it progress? This approach can be taken if there is relatively little risk in waiting a while. Prostate cancer is a very slowly progressing tumor, particularly in older men. Rechecking a mildly abnormal PSA in a few months is a reasonable strategy to follow because the disease is unlikely to progress significantly in that time frame. I could have saved myself two prostate biopsies had I followed that advice. Physicians are so imbued with the desire not to miss anything and to have definitive answers when there is uncertainty, they will often push for a definite diagnosis. It is worth asking what would happen if one just watched for a while before making a decision. Conversely, the outcome of some diseases, like breast cancer, are materially affected by how early one treats the disease. Thus a mammogram suspicious of cancer is not something that one wants to wait to resolve.
The Risks of Further Testing: The low-platelet example showed that a mildly “abnormal” platelet count can lead to a bone marrow biopsy, which is a painful, invasive, and expensive test. Those characteristics in combination with the absence of clinical findings tip the scale in favor of waiting to see if the abnormality disappears or worsens. There are some test results, however, that always require more follow-up. An example, in addition to a mammogram suspicious of cancer, is a heart that appears enlarged on a chest x-ray. Because of the seriousness of the suspected disease, this result requires a more immediate follow-up, and there is a simple, noninvasive and relatively inexpensive way of assessing the problem, an echocardiogram (ultrasound), which can provide a more specific diagnosis. So, in this case, one would not delay in ordering the further test.
The Risks versus Benefits of Treatment: The ultimate goal of testing is to detect a problem that can be treated. Too often, testing for a diagnosis is pursued when the treatment won’t make any difference. A friend of mine was hospitalized for a stroke. He already had many serious problems, and his life expectancy was measured in months. In the hospital, a routine chest x-ray revealed a cavity in the lung — the result of a previous infection that was already known. A logical step in discovering a cavity in the lung is to culture the sputum to see if an organism can be detected that might be causing it. Tuberculosis would be one such organism and in his case, a bacterium similar to tuberculosis was found. However, this bacterium was very slow growing and not likely to spread or to cause serious problems in the months that he had to live. Yet, his physician recommended that he take multiple antibiotics for the next year. Because of the potential side effects of the antibiotics and my friend’s life expectancy, treating this infection made no sense, but the machinery of medical care had identified a problem, and there was pressure to follow it to its resolution. Thankfully, after consultation with his wife, a decision was made not to treat. He died a few months later of other causes.
There is no formula for advising people what to do with an abnormal test, but there are logical questions that patients should ask their physicians. Could this test be an error (false positive)? This is a particularly important question if symptoms or signs do not correlate with the test. If the patient is faced with an invasive procedure as a next step, a logical question is what happens if we watch and wait for a while? What are the risks of performing the follow-up test versus the risk of waiting, or simply treating? Is there a disease for which we are searching that can be treated with benefit to the patient? The answers to these questions will help patients make much better decisions when faced with abnormal test results.
Al Martin, M.D., 75, is a former associate professor of medicine at University of California San Francisco Medical Center and Chief Medical Officer of Blue Shield of California. He now writes a blog, Age With Spirit.