Depending on the virus, it can take weeks for antibodies to develop after exposure to the virus. In these situations, test results may be negative early in the course of the infection. This is called a false-negative test result. Another blood sample may need to be drawn later to check again for a viral infection. Antibody titers that get higher over 3 weeks from the first sample to the second mean the infection occurred recently.
Normal (results that do not show a viral infection are called negative):
No antibodies to the virus are found.
Viral antigen detection test:
No antigens made by the viral infection are found.