I believe the initial screening test has a high % of false pos signals. The Riba test is very specific for antibody and a neg riba is a neg outcome for antibody.
Really haven't studied up much on the antibody tests, but I do know that tests that measure viral load (PCR's, TMA's, etc) will give you a more definitive result as to whether or not you have the virus. The exception is in the beginning of the acute stage when viremia may be intermittent, meaning the viral count may one day be UND and the next day high and the next day UND. During that period, one has to rely on antibody testing, liver enzymes, and other clinical signs to help with the diagnosis.
All the best,
-- Jim