Immunology & Serology Flashcards

What does the RPR test detect?

Answer: Reagin antibodies against cardiolipin-lecithin-cholesterol antigen

RPR is a nontreponemal test that detects reagin antibodies to a cardiolipin antigen released from damaged host cells.

Which test is a treponemal-specific test for syphilis?

Answer: TP-PA

Treponema pallidum particle agglutination (TP-PA) detects antibodies directed specifically against T. pallidum antigens.

In the reverse syphilis screening algorithm, the treponemal EIA is reactive and the RPR is nonreactive. What is the next step?

Answer: Perform a second, different treponemal test such as TP-PA

Discordant results are resolved with a second treponemal test to tell past or treated infection apart from a false-positive EIA.

During the 'core window' of acute hepatitis B, HBsAg has cleared and anti-HBs is not yet detectable. Which marker is positive?

Answer: Anti-HBc IgM

IgM anti-HBc is the only marker detectable during the window period of acute HBV infection.

A patient's results are HBsAg negative, anti-HBc negative, and anti-HBs positive. This pattern is most consistent with:

Answer: Immunity due to hepatitis B vaccination

The vaccine contains only HBsAg, so a vaccinated person makes anti-HBs without anti-HBc.

Which hepatitis B marker indicates active viral replication and high infectivity?

Answer: HBeAg

HBeAg correlates with high HBV DNA levels and greater infectivity.

An undiluted serum gives a negative agglutination result, but a 1:16 dilution of the same serum is strongly positive. This is caused by:

Answer: Prozone phenomenon from antibody excess

In prozone, excess antibody saturates the antigen sites so no lattice forms, which gives a false negative until the serum is diluted.