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quantifying viral load

Oct 5, 2000

Is viral load determined before or after PCR amplification? The reason I ask is that I see "50 perMl" given as the number at which the virus is undetectable, and that would mean that before PCR virtually everyone who is HIV positive is "undetectable".

Response from Dr. Holodniy

A 50 copy viral load is what is there before PCR. An internal standard of known copy number is added to each patients sample of unknown copy number. Based on the signal obtained in a PCR assay for the known standard, the patient copy number is calculated. After PCR there are literally billions of copies of HIV floating around. We could never detect 50 copies without the amplification that PCR affords. So a viral load of 50 copies is a back extrapolation to the starting material.


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