What Affects the Test

Reasons you may not be able to have the test or why the results may not be helpful include taking antiviral medicines.

What To Think About

• Sometimes positive antibody or antigen detection test results are made by organisms other than the virus. This is called cross-reactivity, which leads to a false-positive test result. A test that shows a viral infection may need to be confirmed by additional tests.
• Sometimes an unborn baby (fetus) or newborn baby is tested for several viral infections all at the same time. This is called a TORCH test (for toxoplasmosis, other infections, rubella, cytomegalovirus, and herpes). The TORCH test shows whether a fetus or newborn is likely to have any of these infections.
• Depending on the virus, it can take weeks for antibodies to develop after exposure to the virus. In these cases, 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 the viral infection. Antibody titers that get higher over 3 weeks from the first sample to the second usually mean the infection occurred recently.
• Tests are available that can identify many viruses from one sample of body fluid. For example, one test can identify 12 different viruses that may be causing a lung infection.
• Spinal fluid is collected during a spinal tap (lumbar puncture). For more information, see the topic Lumbar Puncture.
• For more information on specific tests, see the following topics:
  • Human Immunodeficiency Virus (HIV) Test
  • Herpes Tests
  • Hepatitis A Virus Test
  • Hepatitis B Virus Test
  • Hepatitis C Virus Test
  • Human Papillomavirus (HPV) Test
  • Mononucleosis Test