Question

Describe an ELISA test to detect the presence of HIV antibodies in a patient.

Answer 1

The enzyme-linked immunosorbent assay (ELISA), also known as an enzyme immunoassay (EIA), is a screening test for HIV. Blood is the sampe Used in HIV for detection of antibodies.

In the most simple form of an ELISA, antigens from the sample are attached to a surface. Then, a matching antibody is applied over the surface so it can bind to the antigen. This antibody is linked to an enzyme, and in the final step, a substance containing the enzyme's substrate is added. The subsequent reaction produces a detectable signal, most commonly a color change.

In an ELISA test, a person's serum is diluted and applied to a plate to which HIV antigens have been attached. If antibodies to HIV are present in the serum, they may bind to these HIV antigens. A specially prepared "secondary antibody" – an antibody that binds to human antibodies – is then applied to the plate, followed by another wash. This secondary antibody is chemically linked in advance to an enzyme. A substrate for the enzyme is applied, and catalysis by the enzyme leads to a change in color or fluorescence.

Antibody tests may give false negative (no antibodies were detected despite the presence of HIV) results during the window period, an interval of three weeks to six months between the time of HIV infection and the production of measurable antibodies to HIV seroconversion.