Fact: HIV tests for antibodies or the virus itself are highly reliable (both in terms of sensitivity and specificity).
There are two important measures when considering the accuracy of an HIV test or any screening or diagnostic test: sensitivity and specificity.
[1]Two different HIV rapid tests both showing a positive result
Sensitivity is a measure of how likely it is that the test will return positive results if the person being tested has HIV. A highly sensitive test is calibrated to capture every positive sample, but will probably produce some false positives because it is so sensitive that may react to other substances as well.
Specificity is a measure of how likely it is that the test will return negative results if the person being tested does not have HIV. A highly specific test will only react to the substance being tested for and exclude all true negatives, but it will also produce false negatives.
