It’s a scene we see everyday- a worried parent comes to the Radiology Department for an intimidating test on their child. Their pediatrician has requested the exam as part of an attempt to sort out why the child is having headaches, or stomach pain, or a limp. After going through all of the anxiety and sometimes discomfort of the test, taking time out of school or work, and waiting several days to hear back from the pediatrician, the news finally arrives…the test didn’t show anything wrong. The initial relief at not hearing terrible news is quickly replaced by frustration. “I thought this was going to answer our question! How could such an expensive and invasive test not show what the problem was? What do we do now?” These frustrations only increase when the bill arrives; even if the test is covered by insurance, it seems crazy that something so expensive didn’t even address the problem.
In medicine, and in science in general, the value of normal or “negative” results is often discounted. This is a mistake, because a negative test result can remove a huge number of possible explanations from consideration, and we can focus on the few that are left in order to solve the problem. Many tests are ordered with the complete expectation that they will be normal. This doesn’t mean that the symptoms aren’t real- there are lots of conditions that simply don’t show up on radiology tests.
For example, your pediatrician may be fairly certain that your child has tension headaches, caused by the contraction of muscles on nerves on the surface of the skull. She orders an MRI, knowing full well that MR exams in this condition are always normal. She’s getting the test not to confirm the diagnosis of tension headache, but to make sure other much more rare (and less likely) diagnoses no longer have to be considered. She can now proceed with confidence to treat the tension headaches.
Sometimes these “tests of exclusion” are only ordered if a trial of treatment doesn’t work as well as expected, or they may be ordered before treatment because it may take a long time to show results. A significant advance in medicine over the last decade or two has been the ability to look at test results in large numbers of people to determine when the test will have value and when it won’t. It doesn’t mean we won’t continue to do tests that turn out normal, but it means that we will know and appreciate how valuable that normal result really is.
Contributed by Dr. Blaise Jones and edited by Janet Adams, (ADV Tech-US).