In the case of a very recent infection with HIV, the screening test used in the blood donation labs can give negative results, despite the fact that it is indeed contaminated blood. I suspect that one uses PCR for this screening, this should normally be very sensitive to the smallest amounts of nucleic acids? So why does it take ten days before people can see the HIV virus? And besides: if you use pure packed cells (RBC), then there are no white blood cells or plasma in them, and therefore no HIV, right?
Answer
By using molecular tests such as PCR, the ‘window phase’ (the time between infection and its becoming diagnosable) can be reduced (compared to serological testing alone), but not reduced to zero. Initially there are very few viruses present so that they cannot be detected, but still, given the important volumes that an acceptor can receive during transfusion, represent a transmission risk. It is correct that plasma and white blood cells are the source of infection in blood infected with HIV. These are relatively reduced in the preparation of packed RBCs, but again it cannot be guaranteed that the risk of infection is reduced to zero with contaminated blood. A precautionary principle is always applied and a priori excludes potentially contaminated blood, so that the chance that contaminated blood will still be negatively affected by the test battery is minimal.
Answered by
Prof. dr. Dr Bruno Verhasselt
Microbiology and Immunology
http://www.ugent.be
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