Question

Which of these statements is/are correct about competitive ELISA?
(A). It can be used for accurate measurement of the circulating level of the hormone.
(B). There is competition between the natural antigen (hormone) to be tested for and an enzyme conjugated form of the antigen which is the detection reagent.
(C). The more natural antigen present the more it will displace (compete out) the conjugated form leading to a reduction in enzyme bound to the plate.
(D). The more natural antigen bound to the antigen, the higher the signal will be generated.
Choose the correct answer from the options given below:

• A. (A), (B) and (D) only.
• B. (A), (B) and (C) only.
• C. (A), (B), (C) and (D).
• D. (B), (C) and (D) only.

Hint:

In a competitive ELISA:
\[ \text{Signal (color intensity)} \propto \frac{1}{\text{Antigen Concentration}} \] High concentration of the analyte in your sample always results in a low colorimetric signal.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Competitive ELISA is a highly sensitive assay variation used to quantify small molecules, such as hormones, where antibody binding sites are limited.

Step 2: Detailed Explanation:
- Statement (A) evaluation: Competitive ELISA is the preferred choice for measuring low concentrations of circulating hormones because it is highly accurate for small antigens with few epitopes. This is a correct statement.
- Statement (B) evaluation: The principle of competitive ELISA relies on the competition between unlabeled antigen (in the sample) and labeled (enzyme-conjugated) antigen for a limited number of antibody binding sites. This is a correct statement.
- Statement (C) evaluation: If the concentration of the natural (unlabeled) antigen is high, it binds more of the available antibody, displacing the conjugated form. This results in less enzyme conjugate bound to the plate. This is a correct statement.
- Statement (D) evaluation: Because higher concentrations of natural antigen lead to less bound enzyme conjugate, the resulting colorimetric signal is inversely proportional to the antigen concentration. Therefore, more natural antigen leads to a lower signal, making this statement incorrect.

Step 3: Final Answer:
Statements (A), (B), and (C) are correct. This corresponds to option (B).