False Negatives (-) and False Positives (+)!
Any detection test (viral, hormone, antibody, etc.) has a limit of detection which defines how sensitive it is, and an inherent specificity which determines how much it will pick up antigens similar to, but not, the target.
A more sensitive test will result in fewer false negatives -the test is more likely to correctly identify the target even if it’s present in very low quantities.
A more specific test will result in fewer false positives – the test is less likely to recognize things that are not actually the target.
Sensitivity and specificity for a test sit on a spectrum with every test being slightly different! Often they are inversely related, in that the lower the detection limit, the more likely it will pick up incorrect targets and vice versa. When developing an analytical test is important to evaluate where these limits need to be in the context of what is being detected. Are false positives or false negatives of more consequence? It depends and must be determined case by case.