Immunoassay Classifications

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Questions and Answers

What is the main principle behind a competitive assay?

Binding of analytes to fixed sites without competition.

Detection of two analytes simultaneously.

Competition between labeled and unlabeled antigens for binding sites. (correct)

Use of a single labeled antibody for detection.

What is a significant advantage of the sandwich assay?

Ability to detect small antigens easily.

Only a single antibody is needed for detection.

High specificity and sensitivity due to dual antibody binding. (correct)

Low specificity and sensitivity.

Which of the following is a disadvantage of the sandwich assay?

Easily accommodates small antigens.

Requires carefully matched antibody pairs. (correct)

Less resistant to interference from other components.

Can be used without a washing step.

In a competitive assay, the amount of labeled antigen bound to the antibody is:

Inversely proportional to the concentration of the unlabeled analyte. Signup and view all the answers

Which type of assay can use both labeled antigen and labeled antibody?

Homogeneous competitive assay. Signup and view all the answers

What is a major challenge in testing small antigens using the sandwich assay?

Finding two distinct epitopes that do not interfere with each other. Signup and view all the answers

Which sample types are particularly suitable for analysis using sandwich assays?

Complex small samples like serum and plasma. Signup and view all the answers

What is essential for the successful performance of a sandwich assay?

Carefully matched pairs of antibodies that bind to different epitopes. Signup and view all the answers

What is the main principle behind label-free immunoassays?

They depend on the physical properties of the complex to detect binding. Signup and view all the answers

Which of the following is an advantage of label-free immunoassays?

Cost-effectiveness due to lack of labeling procedures. Signup and view all the answers

What is a disadvantage associated with label-free immunoassays?

They have a lower sensitivity compared to labelled assays. Signup and view all the answers

What causes the Hook Effect in label-free immunoassays?

Highly concentrated analytes inhibiting complex formation. Signup and view all the answers

Which method is an example of a label-free immunoassay?

Latex Agglutination Assay (LAA). Signup and view all the answers

What is the role of the standard curve in Latex Agglutination Assays?

To create a reference for quantifying antigen concentrations. Signup and view all the answers

What type of immunoassay is characterized by the use of an excess of reagents to maximize sensitivity?

Reagent excess non-competitive immunoassay. Signup and view all the answers

Which of the following approaches is essential to overcome the Hook Effect in label-free immunoassays?

Conducting appropriate dilutions of the analyte. Signup and view all the answers

Study Notes

Immunoassay Classifications

Label-Free Immunoassays
- These assays don't involve labelling the antibody or antigen.
- Detection relies on physical properties of the antibody-antigen complex, like size or light scattering.
- Antibody or antigen is coated onto cells, binding triggers clumping, forming precipitation or agglutination.
- Advantages include simplicity and cost-effectiveness.
- Disadvantages include lower sensitivity compared to other assays and the possibility of a "hook effect."
- Example: Latex Agglutination Assays (LAAs) use latex beads coated with antigen to detect antibodies. A standard curve is used for analyte concentration validation.

Reagent Excess Immunoassay

Non-competitive
- Uses a surplus of reagents, usually antibodies (Abs).
- Ensures all target analyte in the sample is captured and detected.
- Maximizes sensitivity.
- Suitable for determining analyte concentrations over a wide range.
- Example includes 2-site/sandwich assays.

Reagent Limited Immunoassay

Competitive
- A limited number of binding sites are available.
- Analyte and a labeled form of the analyte compete for the binding sites on the antibody.
- The amount of labeled analyte bound is inversely proportional to the concentration of the analyte in the sample.
- Higher signals indicate lower analyte concentrations.
- Example: The Enzyme Multiplied Immunoassay Technique (EMIT). Glucose-6-phosphate dehydrogenase competes with the analyte, resulting in a signal directly proportional to the concentration of the analyte.

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Description

Explore the various classifications of immunoassays, including label-free and reagent excess methods. Gain insights into their mechanisms, advantages, and limitations, as well as specific examples such as Latex Agglutination Assays. This quiz will provide a comprehensive understanding of how different immunoassays operate.