Final answer:
ELISA tests can detect both antigens and antibodies, utilizing various methods such as direct ELISA for antigens and indirect ELISA for antibodies. The appropriate answer is that ELISA tests do both B and C.
Step-by-step explanation:
Serologic tests based on enzyme-linked immunosorbent assay (ELISA) technology can detect antigens and detect antibodies depending on the variation of the assay employed. In direct ELISA, antigens are immobilized in a microtiter plate and targeted by an antibody that is conjugated to an enzyme. If the antigen is present, the antibody will bind, leading to a color change upon the addition of a substrate. Indirect ELISA, on the other hand, is used to detect antibodies in a patient's serum, with known antigens attached to the plate to capture antibodies from the patient, followed by detection with an enzyme-conjugated secondary antibody. Furthermore, sandwich ELISA, another variation, uses a primary antibody to capture antigens, followed by a secondary antibody with an enzyme that also recognizes epitopes on the antigen, leading to quantification of the antigen after a color change.
The correct answer to whether ELISA tests screen for one organism at a time, detect antigens, detect antibodies, or do both B and C, is that they do both B and C: they detect antigens and they detect antibodies.