Unfortunately, many medical tests just aren’t accurate enough that you can depend on their results without either running an additional test or turning to some other evidence to determine whether you can trust their results. It’s not that there is something wrong with the test; it’s that the test just can’t be accurate enough for some applications.
When tests have been available for many years, their accuracy rates are well known by the doctors who run them. For newer tests, this may not be true.
The key for empowered patients, then, is to ask questions about the accuracy of any tests we are given - before and after we get the results. We want to know, and we want our doctors to be aware, that we want to better understand whether we can trust the results. The trustworthiness of the results will help us determine what we do next.
Some tests have a high rate of false positives
A false positive occurs when a test indicates that yes, a person has a disease or condition - but they don’t really have it. The test comes back positive for whatever the test was looking for. But in fact, it’s an incorrect result.
An example is the CA-125 test, which used to be used to determine if a woman had ovarian cancer. However, because the false positive rate was so high (meaning many women were told they had ovarian cancer when they did not), the CA-125 test is no longer used by itself to diagnose ovarian cancer. It may be used in conjunction with other tests, but it is not used by itself to determine the diagnosis