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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From Google:
> Sensitivity denotes the probability of a positive test result when disease is present. It is calculated as the percentage of individuals with a disease who are correctly categorized as having the disease. A test would be considered sensitive, in general if it is positive for most individuals having the disease.
So theoretically a test that says “positive” for everyone who takes it would detect 100% of the actual positive cases. Now it’s also giving you a ton of incorrect positives too, but the definition of sensitivity used in medical testing doesn’t care about anyone besides the actual positive people. So maybe you are thinking about how “sensitive” in common language usually just means “good at finding what we are looking for”, but that’s not the definition they are using in this context.
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