How Accurate Are Your Medical Test Results?

Checking Their Accuracy May Make a Huge Difference in Your Healthcare

A doctor looks into a microscope.
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Every day, we patients are given medical tests and we trust that they are accurate. The results determine whatever happens next. We may be diagnosed with something new or prescribed a new treatment. A treatment may be changed, or maybe we'll be declared cured of whatever our medical problem was. The results might suggest we just keep doing what we've been doing.

What most of us don't realize is that not all test results are correct or accurate. Incorrect or inaccurate test results may lead to a misdiagnosis, a missed diagnosis or a failure to diagnose. We may have something wrong and not get treated for it or we may suffer through treatment for something we didn't really have.

Reasons for Wrong Medical Test Results

There are many reasons medical test results might be wrong. Mistakes are made with how specimens are handled, paperwork can get mixed up. There can problems with how the test was administered or whether the equipment used was calibrated correctly. The tests themselves may have problems with the accuracy.

There isn't much we can do to prevent the first three reasons because they are due to circumstances beyond our control. The only way to protect ourselves from having to deal with the outcomes of those mistakes is to ask to have the same test run again, in order to confirm the findings or show that the original findings were incorrect.

But that last reason they may be wrong — a problem with accuracy — has to do with the quality of the test and its results. Few medical tests, even those run and reviewed perfectly, deliver the right results 100% of the time. Many are highly accurate, but even those tests have a failure rate, although it might be very small.

Medical Test Accuracy

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.

Here are some of the considerations scientists and doctors use to determine medical test accuracy:

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.

My own misdiagnosis story is an example of a false positive carried to an extreme.

Some Tests Have a High Rate of False Negatives

The test result indicates that a person does not have whatever was being tested for. But in truth, they do have it. Mammograms are known for having high rates of false negatives (and false positives). While some of the false negative results stem from inaccuracy in reading the scans, other errors come from the sensitivity of the equipment.

There are additional considerations that tie into determining false positives and false negatives. They are related to two other concepts — sensitivity and specificity.

But the bottom line is, the potential for mistakes must be considered when it comes to trusting the test results and then deciding what steps we will take next.

Questions to Ask About Your Medical Test Results

When you are provided with test results that will influence decisions about your next steps - or which the doctor will rely on for changing his or her recommendations - here are some questions you can ask (or do some Internet research) to determine the accuracy and trustworthiness of the results.

  • How often does this test produce false positives?
  • How often does this test produce false negatives?
  • How confident are you (the doctor) that the results are accurate?

If the doctor gives you any indication that your results could at all be inaccurate, ask:

  • Are you confident enough in the results that you would ask your mother or father to undergo the treatment you are recommending for me?
  • Is there another test we can run to see if it supports or confirms these results?

The doctor's answers, and your research, will help you make your next important medical decision.

One last piece of advice: Don't forget to get copies of your test results.

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