The immune system is the body’s defense against diseases. It can detect foreign body and other harmful substances and once detected would do the necessary response to remove them from the bloodstream.

The immune system releases antigens, a substance that activates the body’s white blood cells or the army cells, which will then produce proteins/antibodies that find and attach to specific antigens to remove them.

image above shows how a radioimmunoassay is done

If you want to measure the level of a specific antigen in the blood of the patient, then there are plenty of ways to do so and one of which is radioimmunoassay. A radioactive version of a specific antigen is used to find out how many antigens a person has in the bloodstream. (1, 2, 3, and 4)

Image 1: The image above shows how a radioimmunoassay is done.
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What is radioimmunoassay? 

It is a type of immunological assay that analyses the presence of antigen in a highly sensitive sample. It can determine any biological sample for a particular antibody exist.


Advantages  of radioimmunoassay

  • It can determine the presence of antigen even in a small sample size.
  • It is the most sensitive and specific type of immunoassay.
  • It is a sensitive method that can detect the concentration of antigen without the need for bioassay. It has the ability to measure one trillion of grams of material per milliliter of blood. (3, 4, and 5)
Rosalyn Yalow was the one who developed radioimmunoassay procedure in 1959

Image 2: Rosalyn Yalow was the one who developed radioimmunoassay procedure in 1959. She is a co-winner of the Nobel Prize in Physiology or Medicine (1977) (along with Andrew Schally and Roger Guillemin)
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Radioimmunoassay was developed by Rosalyn Yalow and Solomon Berson in 1959. Their purpose at that time was to measure the level of insulin in plasma. It turned out that the level of hormone in the blood could be checked by an in-vitro assay. (5, 6)

These are the reagents used in performing radioimmunoassay procedure

Image 3: These are the reagents used in performing radioimmunoassay procedure.
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What are the reagents used in performing radioimmunoassay?

  • Tracer
  • Binder/antibody/specific antiserum
  • Standard (pure form)
  • Free human antiserum
  • Separation method (separate bound and free phases)


Principle  of radioimmunoassay

Radioimmunoassay’s high sensitivity is based on these principles – strong binding reaction consists of antigen vs antibody reaction. Its specificity is based on competitive binding reaction and radio emission. (2, 4, and 7)

There are three basic based principles for radioimmunoassay that give it a high sensitivity such as the strong immune binding reaction of antigen and antibody, competitive binding reaction, and radio emission.  (7, 8, and 9)

Radioimmunoassay is used in a variety of industries such as pharmacology, disease diagnosis, detection of allergies, and the likes

Image 4: Radioimmunoassay is used in a variety of industries such as pharmacology, disease diagnosis, detection of allergies, and the likes.
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Radioimmunoassay (RIA) Procedure – Animation video

What are the uses of radioimmunoassay?

  • It is used to determine a small number of antigens and antibodies in a particular serum.
  • It is useful in quantifying of hormones, HBsAg, drugs, and other forms of viral antigens.
  • It can check the concentration of picomolar and nanomolar hormones in biological fluids.
  • It is used in the analysis of vitamins and other metabolite markers.
  • Radioimmunoassay can diagnose any type of allergy.
  • It has the ability to detect and diagnose cancer.
  • In the blood bank, radioimmunoassay is used to track and screen leukemia and hepatitis virus, which is highly contagious.
  • It is used to diagnose and treat peptic ulcers.
  • It plays a fundamental role in the research of neurotransmitter, a chemical in the brain. (2, 6, 9, and 10)
These are the base kit when performing radioimmunoassay

Image 5: These are the base kit when performing radioimmunoassay.
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What is needed in performing radioimmunoassay?

  • Specific antiserum for the antigen to be checked
  • Radioactively labeled form of antigen
  • A technique that can separate antibody-bound tracer from unbound tracer
  • Instrument that can count radioactivity (2, 5, and 8)


  1. A specific quantity of antigen is made radioactive.
  2. The radiolabeled antigen is mixed with a specified amount of antibody for a particular antigen causing the two to bind to each other.
  3. A serum sample from a patient that contains an unknown quantity of the same antigen is added causing the unlabeled antigen from the serum to compete with the radiolabeled antigen for the antibody binding sites.
  4. The unlabeled antigen concentration increases causing it to bind more to the antibody.
  5. The radiolabeled variant is displaced reducing the ratio of antibody-bound radiolabeled antigen.
  6. The bound antigen separates from the unbound ones.
  7. The remaining free antigen’s radioactivity in the supernatant is measured. (4, 8, 9, and 10)

What are the disadvantages/limitations?

  • The reaction time could take days/prolonged reaction time. Hence, it warrants the use of a highly diluted reagent.
  • Handing of radioisotopes could cause possible health hazards.
  • It is important to make sure that all reagents are precisely added.
  • Limited assay range.
  • Automation can be a bit difficult.
  • Counting time can be a lengthy process.
  • There is no direct linear relationship between the concentration of analyte and signal response.
  • The equipment and reagents used are pricy.
  • The radiolabeled compounds have a short self-life.
  • Since it is radioactive, there’s some sort of a problem in disposing of radioactive waste. (3, 4, 8, and 10)

Radioimmunoassay is an old assay method. However, it is still used even up to these modern times as it offers more advantages over other methods, especially when it comes to sensitivity and simplicity.

Is radioimmunoassay different from ELISA?

Radioimmunoassay and ELISA are two different procedures. ELISA is a procedure in which the color is produced secondary to an immune reaction. The qualitative and quantitative analysis is done based on color. In the radioimmunoassay procedure, the immune reaction is measured through the presence of radiation.

Between the two, ELISA is highly preferred as it is yields to a more accurate result. ELISA is a highly sensitive procedure and more specific in detecting substances in the body when compared with other methods of detection. Although radioimmunoassay and ELISA are different procedures, they share some common traits such as their usage in research and diagnosis and principles. (1, 4, 6, and 7)



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