I have searched prior posts and I haven’t seen a good explanation that seems to help my seemingly tiny brain grasp this concept.
Highly sensitive tests rule OUT a disease. To me, this means if the test is negative, it’s likely to be a true negative because you are pretty certain that it’s an accurate negative result.
However, I just did a review question that told me sensitivity detects true positives and now I’m confused.
For example, D-dimer is a highly sensitive test. If it’s not elevated, we feel fairly certain the disease we are ruling out is ruled out. Wouldn’t this be a true negative? (Obviously not according to the world, but can someone please ELI5??)
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Sensitivity is proportion of people tested positive within the positive population. So high sensitivity implies people who are positive are not likely tested negative. When we want to rule out a disease we are trying to make sure people having the disease don’t get false negatives, ie a test with high sensitivity. But on the other hand many people with no disease may also get a positive result. Eg try to imagine asking a person if he is tired to know if he had enough sleep last night, if one said he is not tired you’d know one likely had enough sleep, but tons of other people (eg someone right after workout) may feel tired but had enough sleep
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