A viral test is done to find
infection-causing viruses. Viruses grow only in living cells. Viruses cause
disease by destroying or damaging the cells they infect, damaging the body's
immune system, changing the genetic material (DNA) of the cells they infect, or causing inflammation
that can damage an organ. Viruses cause many types of diseases, such as
human immunodeficiency virus (HIV),
measles, flu (influenza), and some types of
Viral tests may be done for viruses such as:
Several types of tests may be used to check for
Different types of samples are used for a viral test,
including blood, urine, stool (feces), organ tissue, spinal fluid, and saliva.
The type of sample used for the test depends on the type of infection that may
A viral test is done to:
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
Samples can be collected in several
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 antigens are
Changes occur in the culture
that show a viral infection.
Viral DNA or RNA detection
Viral DNA or RNA is
Reasons you may not be able to
have the test or why the results may not be helpful include taking antiviral
To learn more about a
specific test, see:
Other Works Consulted
Fischbach FT, Dunning MB III, eds. (2009).
Manual of Laboratory and Diagnostic Tests, 8th ed.
Philadelphia: Lippincott Williams and Wilkins.
Pagana KD, Pagana TJ (2010). Mosby’s Manual of Diagnostic and Laboratory Tests, 4th ed. St. Louis: Mosby Elsevier.
December 30, 2011
E. Gregory Thompson, MD - Internal Medicine
& W. David Colby IV, MSc, MD, FRCPC - Infectious Disease
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