Which of the following is characteristic of an indirect enzyme immunoassay?

Which of the following is characteristic of an indirect enzyme immunoassay?

• A. The first antibody has the enzyme label.
• B. Color is directly proportional to the amount of patient antigen present.
• C. All reagents are added together.
• D. Enzyme specificity is not essential.

Answer: (B)

An indirect enzyme immunoassay is designed to detect antibodies in the patient's serum. The plate is coated with the antigen of interest, and if the patient has specific antibodies, they bind to that antigen. A secondary antibody that recognizes human antibodies and carries an enzyme is then added; it binds to the patient antibodies, and when a substrate is added, a color develops. The intensity of that color reflects how much patient antibody was present and bound to the antigen, not the amount of antigen itself. This is why the key characteristic is that the color is proportional to the amount of patient antibody. The first antibody is not enzyme-labeled in this setup—the enzyme label is on the secondary anti-human antibody. Not all reagents are added simultaneously, and enzyme specificity is essential for producing a meaningful color signal.

An indirect enzyme immunoassay is designed to detect antibodies in the patient's serum. The plate is coated with the antigen of interest, and if the patient has specific antibodies, they bind to that antigen. A secondary antibody that recognizes human antibodies and carries an enzyme is then added; it binds to the patient antibodies, and when a substrate is added, a color develops. The intensity of that color reflects how much patient antibody was present and bound to the antigen, not the amount of antigen itself. This is why the key characteristic is that the color is proportional to the amount of patient antibody.

The first antibody is not enzyme-labeled in this setup—the enzyme label is on the secondary anti-human antibody. Not all reagents are added simultaneously, and enzyme specificity is essential for producing a meaningful color signal.