Labeled Immunoassay

• What is required to visualize reactions in precipitation and agglutination?

  Different equipment and sufficient concentration
• What is the purpose of labeled immunoassays?

  To detect small amounts of antigens or antibodies
• Why are they called "labeled" immunoassays?

  They use labeled substances like enzymes or radioisotopes
• What is an analyte in labeled immunoassays?

  Substance being measured
• Give examples of analytes.

  Bacterial antigens, tumor markers, hormones
• What is the role of antibodies in labeled immunoassays?

  To react with the analyte for measurement
• What should be true about antibodies and antigens in these assays?

  They should be specific to each other
• What is the purpose of using different machines in labeled immunoassays?

  To read the reaction results
• What is the characteristic of antibodies in labeled immunoassays?

  High affinity for the antigen
• How does the affinity of antibodies affect immunoassays?

  Higher affinity leads to more accurate measurements
• What are standards or calibrators in immunoassays?

  Unlabeled analytes with known concentrations
• What is the role of standards in immunoassays?

  To establish relationships between labeled and unlabeled analytes
• What are some separation methods used in labeled immunoassays?

  Decanting, centrifugation, filtration
• What is the purpose of washing steps in separation methods?

  To remove unbound analyte
• How is the label detected in radioimmunoassays?

  By counting radioactivity
• What is measured in enzyme-linked immunoassays?

  Change in absorbance of a substrate
• What is the purpose of quality control in immunoassays?

  To check the quality of reagents
• What should be run with every test for quality control?

  A blank tube with phosphate-buffered saline
• What are the two major formats of labeled immunoassays?

  Competitive and noncompetitive immunoassays
• How do competitive immunoassays work?

  Reactants are mixed; labeled competes with unlabeled
• What does the amount of bound label indicate in competitive immunoassays?

  It is inversely proportional to labeled antigen concentration
• What happens when there is no patient antigen in competitive immunoassays?

  Only labeled antigen binds to the antibody
• What is the process in noncompetitive immunoassays?

  Patient antigen binds first, then labeled antibody
• How is the amount of label measured in noncompetitive immunoassays?

  It is directly proportional to patient antigen amount
• What distinguishes heterogeneous assays from homogeneous assays?

  Heterogeneous assays require a separation step
• What is the principle of heterogeneous enzyme immunoassays?

  Competitive binding of labeled and unlabeled antigens
• Who pioneered radioimmunoassay?

  Yalow and Berson
• What is the principle of radioimmunoassay?

  Competitive binding
• What is a significant application of radioimmunoassay?

  Measuring small amounts of hormones
• What is the most common radioactive substance used in radioimmunoassay?

  125 Iodine/Iodine 125
• What are the disadvantages of using radioactive substances?

  Health hazards and disposal problems
• What is the radioallergosorbent test (RAST) used for?

  Measuring antigen-specific IgE
• What is the radioimmunosorbent test (RIST) used for?

  Quantitating total IgE
• What are enzyme immunoassays developed as an alternative to?

  Radioimmunoassays
• Why are enzymes preferred as labels in immunoassays?

  They are cheaper and readily available
• What is the principle of competitive enzyme immunoassays?

  Enzyme-labeled antigen competes with unlabeled antigen
• What is the principle of noncompetitive enzyme immunoassays?

  Label binds after antigen-antibody reaction
• What does the amount of color or fluorescence indicate in noncompetitive enzyme immunoassays?

  It indicates the amount of patient antigen
• What are the two enzymes most commonly used in assays?

  Horseradish peroxidase and Alkaline phosphate
• Why are horseradish peroxidase and alkaline phosphate preferred in assays?

  They have the highest turn-over rate