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), cold sores, chickenpox, measles, flu (influenza), and some types of cancer.
Viral tests may be done for viruses such as:
Several types of tests may be used to check for viruses:
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 be present.
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 your test.
Samples can be collected in several ways.
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 infection-causing viruses.
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 titres. A titre 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 titres 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.
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):
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 found.
Changes occur in the culture that show a viral infection.
Viral DNA or RNA is found.
Reasons you may not be able to have the test or why the results may not be helpful include taking antiviral medicines.
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.
Current as ofJune 25, 2018
Author: Healthwise StaffMedical Review: E. Gregory Thompson, MD - Internal MedicineAnne C. Poinier, MD - Internal MedicineAdam Husney, MD - Family MedicineMartin J. Gabica, MD - Family MedicineW. David Colby IV, MSc, MD, FRCPC - Infectious Disease
Current as of: June 25, 2018
E. Gregory Thompson, MD - Internal Medicine & Anne C. Poinier, MD - Internal Medicine & Adam Husney, MD - Family Medicine & Martin J. Gabica, MD - Family Medicine & W. David Colby IV, MSc, MD, FRCPC - Infectious Disease
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