Types of Immunoassay: A Comprehensive Guide to Diagnostic Testing

Immunoassays are laboratory techniques used to detect and measure the presence of specific substances in biological samples. They rely on the interaction between antigens (substances that elicit an immune response) and antibodies (proteins produced by the immune system). There are various types of immunoassays, each with its own principles and applications. Here are some common types:

1. Enzyme-Linked Immunosorbent Assay (ELISA)

ELISA is a widely used immunoassay technique. It involves the use of an enzyme-linked antibody to detect and quantify the presence of an antigen. ELISA can be used to detect various substances, such as proteins, antibodies, hormones, and infectious agents.

2. Radioimmunoassay (RIA)

RIA is an immunoassay technique that uses radioactive isotopes to label antigens or antibodies. It measures the amount of radioactivity associated with the antigen-antibody complex, allowing for the quantification of specific substances. RIA has been used in various fields, including endocrinology and cancer research.

3. Immunofluorescence Assay (IFA)

IFA utilizes fluorescent-labeled antibodies to detect the presence of specific antigens. The fluorescent signal emitted by the antibody-antigen complex is visualized using fluorescence microscopy. IFA is commonly used in diagnostic tests for autoimmune diseases and infectious agents.

4. Chemiluminescent Immunoassay (CLIA)

CLIA utilizes chemiluminescent-labeled antibodies to detect specific antigens. The reaction between the labeled antibody and antigen produces light, which is measured to determine the presence and concentration of the target substance. CLIA is known for its high sensitivity and wide dynamic range.

5. Lateral Flow Immunoassay (LFIA)

LFIA, also known as rapid or point-of-care tests, is a simple and portable immunoassay format. It utilizes capillary action to transport the sample and reagents across a porous membrane. The appearance of a colored line indicates the presence of the target antigen. LFIA is commonly used for rapid diagnostic tests, such as pregnancy tests and infectious disease screening.

6. Western Blot

Western blot is a technique used to detect specific proteins in a sample. It involves separating proteins based on their size using gel electrophoresis, transferring them onto a membrane, and then using specific antibodies to bind to the target protein. The bound antibodies are visualized using enzymatic or fluorescent detection methods.

These are just a few examples of immunoassay techniques. Each type has its own advantages, sensitivity, and applications. Immunoassays are widely used in medical diagnostics, research laboratories, and various fields of healthcare to detect and quantify a range of substances, including hormones, antibodies, infectious agents, drugs, and biomarkers.