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Guilherme Mazui

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What is the Difference Between Radioimmunoassay and Immunoradiometric Assay?

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Radioimmunoassay (RIA) and Immunoradiometric Assay (IRMA) are both immunoassays that use radiolabeled components to detect and quantify specific macromolecules in a sample. However, there are some key differences between the two methods:

  1. Reaction: In RIA, the sample or compound to be measured displaces another antigen gradually over some period, while in IRMA, the sample or compound combines immediately with the radiolabeled antibodies.
  2. Sensitivity: IRMA is known for its improved sensitivity compared to conventional RIA. For example, when measuring serum prostatic acid phosphatase, IRMA showed excellent precision over a much wider working range (0.25-1000 micrograms/l) than RIA.
  3. Assay Time: IRMA can be completed in a shorter time (5 hours) compared to RIA, which requires 3 days for completion.
  4. Comparison of Results: When measuring prostatic acid phosphatase in serum, IRMA and RIA results were highly correlated (r = 0.97), but IRMA results were generally lower than those obtained by RIA.

In summary, while both RIA and IRMA use radiolabeled components to detect and quantify specific macromolecules in a sample, the key differences lie in the reaction mechanism, sensitivity, assay time, and comparison of results.

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  • What is the Difference Between Radioimmunoassay and Immunoradiometric Assay?
  • Comparative Table: Radioimmunoassay vs Immunoradiometric Assay

    • Comparative Table: Radioimmunoassay vs Immunoradiometric Assay

    Here is a table comparing the key differences between Radioimmunoassay (RIA) and Immunoradiometric Assay (IRMA):

    Feature Radioimmunoassay (RIA) Immunoradiometric Assay (IRMA)
    Description An immunoassay that uses radioactive elements to detect the amount of antigen in a sample. An immunoassay that uses radiolabeled antibodies to determine antigen levels in a sample.
    Radioactive Elements Radioactive antibodies are used. Radioisotopes are used to label antibodies.
    Competitive Binding A radioactive antigen competes against a non-radioactive antigen for a constant amount of antibody. The sample or compound immediately combines with the radiolabeled antibodies.
    Assay Procedure The sample or compound to be measured is combined with a radioactive antigen before the combination. The sample or compound is combined immediately with the radiolabeled antibodies.
    Precision Precision varies depending on the specific assay conditions. IRMA shows excellent precision over a wider working range than RIA.
    Completion Time RIA typically requires more time, around 3 days. IRMA can be completed in less time, typically 5 hours.
    Sensitivity RIA is very specific and highly sensitive. IRMA generally has a higher sensitivity.
    Correlation with RIA In some cases, such as measuring serum prostatic acid phosphatase, IRMA results may be generally lower than those obtained by RIA, but the two methods correlate well.

    In summary, the main difference between RIA and IRMA is that RIA uses radioactive antibodies and relies on competitive binding, while IRMA uses radiolabeled antibodies and has a more immediate combination with the sample or compound. IRMA tends to have better precision, sensitivity, and faster completion time compared to RIA.

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    Guilherme Mazui

    Guilherme Mazui is graduated in journalism from the Federal University of Minas Gerais (UFMG) and a master's degree in Communication from the University of São Paulo (USP). In addition, he has experience in advertising writing and has worked as a content editor in several companies.