Flu shots & false positive on viral load tests
Nov 22, 2002
I am a middle age heterosexual male. I had unprotected sex single woman 11 weeks ago. My physician gave me a viral load test 2 weeks ago, but he gave me a flu shot about 5 minutes before in the other arm. My viral load test came out positive -- at about 100. He told me that it should be below 50. What are the chances that the flu shot gave me a false positive?
Response from Mr. Kull
It's hard to interpret test results without more information. I can't tell you what effect a flu shot given five minutes before a viral load test will have. Vaccinations could yield an indeterminate result on an antibody test (this is conjecture, and probably unusual), but viral load testing is a different testing method that does not measure antibody production. It's probably not correlated.
Why the viral load test? Are you at significant risk? Were you attempting to determine if your symptoms were indicative of primary infection (recent exposure)? All of these questions are crucial in interpreting results.
Viral load tests conducted during the acute phase of infection (when someone is experiencing symptoms approximately 2-4 weeks after infection) should yield a high viral load (>100,000 copies/mL). Any results that are below 10,000 copies/mL are usually not indicative of HIV infection (ie, false positive).
If the viral load test was conducted well after the window period, antibody testing should accompany it. That will give you a more accurate answer.
PCR tests are not indicated for screening for infection in the general population because of the higher rate of false positives when compared to antibody testing technologies. If you are at low-risk for infection, the PCR result does not say all that much, you should not jump to any conclusions, and you need to have an antibody test.
If you are at significant risk for infection and are within the window period, continue to talk with your doctor about testing alternatives. You should still have an antibody test conducted for baseline.
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