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PCR versus traditional
Mar 6, 2000
Does the PCR test used to measure HIV genetic material in blood have a "window period" like the traditional "antibody" test does?
I've heard two different views. One (the person administering the test) said 8 weeks. Someone else said it was pretty immediate since the same technology is used to measure viral load.
Can you clarify?
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Response from Dr. Squires
The traditional antibody test relies on the presence of antibodies to HIV that have been manufactured by B cells (a type of immune system cells) in response to an infection with HIV. It usually takes 10-14 days for the manufacturing system to be turned on and revved up to produce antibodies.
The PCR (polymerase chain reaction) is one of 2 types of assays that detects viral RNA or DNA, depending on the particular assay. The one that you mention is used to measure the number of HIV virus particles (therefore RNA) in the blood. Since this assay directly detects the virus rather than the result of an immune system response, it will become positive (measure viral particles) before the antibody test will become positive. However, there is another test, the HIV antigen test, that is also used to make the diagnosis of acute infection. It detects p24 antigen (a part of the core of the virus); it is another test that directly detects the virus rather than antibodies.
Hope that this has been helpful.
Kathleen E. Squires, M.D.
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