Blog Post

Immunoassays Explained

23 June 2015

Immunoassays Explained

An Immunoassay is a chemical test used to detect or quantify a specific substance using an immunological reaction. Due to the use of antibodies and purified antigens, immunoassays are very sensitive and specific.

Immunoassays can be qualitative or quantitative, with the first being used in situations such as determining if a woman is pregnant (which can be detected within 2 days of fertilization), and the second is used to determine the concentration of an analyte (which measures the strength of a signal produced by indicator reactions).


The Immunoassay Principle

The principle behind the Immunoassay test is the use of an antibody that will specifically bind to the antigen of interest.

 The antibodies used in the Immunoassay must have a high affinity for the antigen. The antibodies used in the Immunoassay can either be monoclonal or polyclonal antibodies.

 The difference between the two antibodies are:

·      Monoclonal antibodies only bind to very specific antigens and therefore give more accurate and specific results, but these antibodies tend to be more expensive.

·      Polyclonal antibodies are inexpensive but can recognise multiple epitopes on an antigen or they can recognize multiple antigens and these antibodies tend to be less specific.



The most common immunoassay today is the ELISA test.

ELISA or Enzyme-Linked Immunosorbent Assays detect concentrations of the antigen of interest. It is widely used to test blood samples for the presence of viruses such as HIV.



EIA stands for enzyme immunoassay, which means that the antibody that is used to detect the antigen of interest is labeled with an indicator enzyme that enables very small quantities of the antigen of interest to be detected.

 RIA stands for radioimmunoassay, which uses a radioisotope to detect the antigen of interest.

RIA is used when screening blood for the Hepatitis B antigen. Although the problem with RIA is that it is a labor-intensive process and raises several safety issues.


Why we need immunoassays

Immunoassays can detect antigens of interest in very low concentrations that cannot be measured by standard tests. Immunoassays are generally quick and specific which enables a clinician to quickly and accurately diagnose a range of diseases such as diabetes, cancer and heart disease.

Do you want to know more Immunoassays and why we need them? Then please e-mail our team at Lorne Labs HQ and a member of our team will be happy to assist you.

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