Viral Tests
Results
A viral test is done to find infection-causing viruses.
It may take as little as one day or up to several weeks to get test results.
The results of some viral tests (antibody or antigen tests) may be shown in titres. A titre is a measure of how much the sample can be diluted before the viral antibodies or antigens can no longer be seen.
A titre of 1 to 8 (1:8) means that antibodies or antigens can be found when 1 part of the blood sample is diluted by up to 8 parts of a salt solution (saline). A larger second number means there are more antibodies in the fluid sample. Therefore, a titre of 1 to 128 means more viral antibodies or antigens in the fluid sample than a titre of 1 to 32.
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 titres that get higher over 3 weeks from the first sample to the second, mean the infection occurred recently.
Viral test Normal (results that do not show a viral infection are called negative):
Antibody test:
No antibodies to the virus are found.
The antibody titre does not get higher over time, so this infection occurred in the past.
Viral antigen detection test:
No antigens made by the viral infection are found.
Viral culture:
No viral infection is seen in the culture.
Viral DNA or RNA detection test:
No viral DNA or RNA is found.
Abnormal (results that show a viral infection are called positive):
Antibody test:
Antibodies to a virus are found.
Viral antigen detection test:
Viral antigens are found.
Viral culture:
Changes occur in the culture that show a viral infection.
Viral DNA or RNA detection test:
Viral DNA or RNA is found.
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| Author: | Douglas Dana Jan Nissl, RN, BS | Last Updated: October 11, 2006 |
| Medical Review: | Martin Gabica, MD - Family Medicine Adam Husney, MD - Family Medicine W. David Colby IV, MSc, MD, FRCPC - Infectious Disease | |
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| Topic Contents | |
| Test Overview | |
| Why It Is Done | |
| How To Prepare | |
| How It Is Done | |
| How It Feels | |
| Risks | |
 | Results |
| What Affects the Test | |
| What To Think About | |
| References | |
| Credits | |