What is the meaning of 'false positive' and 'false negative' when talking about health?

Means there was a test done and now it is understood that the test was wrong. i.e. a pregnant woman uses a pregnancy test and it shows up negative then sees her doctor and found out the test was a false negative.

In medicine or health, false positives and false negatives are commonplace. A good definition of either is when a test detects something when in fact it is not present giving an incorrect result. This can happen with pregnancy, HIV tests, Drug tests, blood tests, pap smears or colposcopy, software tests where a good file is said to be corrupt or containing a virus or tests on an unborn fetus finding a problem, then not finding it.

Usually there is an underlying reason why you get an untrue answer. Sometimes a high white blood count because of a common cold can make you positive on an HIV test. There are many reasons why this occurs, which is why many people take certain tests more than once.

The term is used in medicine, and there is a variation of the same concept in statistics, but 'false positive' is not the term used.

You may have blood work done some time, and there is any number of possible tests that can be done to check any number of things. Those tests are not absolutely flawless.

Now and then, you will have a test done and the results will come back indicating a positive result-- according to the test, for example, you have a certain kind of antibody in your blood indicating that you have been exposed to a certain infection. But there is a certain percent of the time that the test will give a positive indication where the antibody is in fact not in your blood. There is also a certain percent of the time that the test will come back negative even when the antibody really IS in the blood.

It's hard for us to imagine that anything 'medical' like a blood test can be anything but perfect. Different tests have different margins of error, and it depends on a lot of factors. What is the fluid or tissue that is used for the test? Do other things in my system that are seemingly unrelated to the test somehow influence how the reagents interact with the tissue sample? One example that is not far-fetched is that if you eat a lot of poppy seeds (in muffins or rolls) you might test positive for opiates.