False-Positive / False-Negative

False-positive means the test result came out “positive,” indicating you have that condition, but it was wrong.ย  Vice versa with false-negative: it looks like you don’t have the disease, but the test was wrong, so you really do.ย  It’s not that the lab or radiologist made a mistake with the blood test or x-ray.ย  Rather, many tests are simply not 100% accurate, through nobody’s fault.ย  So when a test is “positive” or “negative,” we clinicians to use our judgment, & consider all information.

We also use the terms “Sensitivity” and “Specificity” in this regard. A test that’s very sensitive (high Sensitivity) has very few false-negative results. So if your result is indeed negative, you can feel comfortable knowing you don’t have that disease. Analogously, a test that’s very specific (high Specificity) has very few false-positive results. So if yours come out positive, it’s highly likely that you do, indeed, have that condition.

Sometimes it’s better not to do tests!ย  There’s a fatal flaw to the idea, “Let’s do the test ‘just in case’.” See topic Why Not to Test People for Unlikely Conditions.

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