I performed HIV, HIV2,
HTLV-
I and
HTLV-II testing in the late 1990's. Surely testing methods have changed a lot since then, but the very basics of immunology have not. Way back in 1998, the generalized "panel" screen for both HIV, HTLVI&II was an antibody test...a patient's serum would be tested against an antigen-coated well plate. If the serum bound with the well, it meant there were antibodies in the serum, which indicated that person tested positive for the virus.