6. False-positive test results happen more often than you might think
The first screening test for a condition often has to be checked by a second, more specific test to find out whether the results are accurate and meaningful for your health. An example is the rapid HIV test, for which false positives are common. In communities where about 1 percent are infected with the virus, two false positive HIV rapid test results are expected for every 10 true positive results, according to the U.S. Centers for Disease Control and Prevention.
Although mix-ups of patient blood test samples are rare, they do happen.
7. False-negative test results happen too
Sometimes a test doesn’t pick up evidence of a disease or condition even though you actually do have it. For example, if you had a blood test for hepatitis C and the results came back negative, but you were exposed to the virus in the past few months, you could still have an infection and not realize it. Getting tested again is a good idea, recommends nurse Lucinda K. Porter, RN, if you think you were recently exposed to this infectious disease.