Why It Is Done
A viral test is done to:
- Find a viral infection that is causing
- Check a person after exposure to a virus. For example, a
viral test may be done after a health professional is accidentally stuck with a
needle containing contaminated blood to see if he or she became infected with the virus.
- Find a
viral infection in a potential blood donor to prevent the donation of infected
- Find a viral infection in an organ to be
- Test a pregnant woman who has a high risk of passing
a serious viral infection on to her baby.
- Check if a person has
immunity to a specific virus.
How To Prepare
Preparations for a viral test depend
on the type of infection that may be present and the sample that will be
tested. Your health professional will give you any specific instructions before
How It Is Done
Samples can be collected in several
- A blood sample can be taken from a vein in the
- A tissue sample can be taken directly from the infection, such
as a throat swab or skin scraping.
- A sample of stool, urine, or
nasal washings may be taken.
- A sample of spinal fluid can be taken
lumbar puncture (spinal tap).
biopsy sample may be taken using a needle or other
How It Feels
The amount of discomfort or pain you
feel depends on the method used to collect a sample for the test. Generally, a
viral test does not cause pain or the pain goes away after the test.
Generally, the chance of problems from the test
depends on the method used to collect a sample for testing. Your doctor can talk to you about any specific risks of the test.
A viral test is done to find
It may take as little as 1 day or up
to several weeks to get test results.
The results of some viral
tests (antibody or
antigen tests) are reported in titers. A titer is a
measure of how much the sample can be diluted before the viral antibodies or
antigens can no longer be detected.
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
No antibodies to the virus are
Viral antigen detection
No antigens made by the viral
infection are found.
No viral infection is seen in
RNA detection test:
No viral DNA or RNA is
Abnormal (results that show a viral infection are called
Antibodies to a virus are
found. But if you have a second antibody test and the results are not higher than the first test, this may mean the infection occurred in the past and is not a problem now.
Viral antigen detection
Viral antigens are
Changes occur in the culture
that show a viral infection.
Viral DNA or RNA detection
Viral DNA or RNA is