Labeled Immunoassays Flashcards
Labeled Immunoassays
○ Are designed for antigens and antibodies that may be small in size or present in very low concentrations
Competitive Immunoassays
○ All the reactants are mixed together simultaneously
○ The labeled antigen competes with unlabeled patient antigen for a limited number of antibody-binding sites
Noncompetitive Immunoassays
○ Antibody is first passively absorbed to a solid phase
Radioimmunoassay
○ The amount of label in the bound phase is indirectly proportional to the amount of patient antigen present
Enzyme Immunoassays
○ Use enzymes as labels, which react with suitable substrates to produce breakdown products that may be chromogenic, fluorogenic, or luminescent
Heterogeneous EIAs
○ Require a step to physically separate free analyte from bound analyte
Capture assays
○ Are best suited to antigens that have multiple determinants
○ Excess antibody attached to the solid phase is allowed to combine with the test sample to capture any antigen present
Homogenous EIAs
○ These antigen–antibody systems do not require a washing or separation step
○ Enzyme activity is directly in proportion to the concentration of patient antigen or hapten present in the test solution
○ Are less sensitive than heterogenous assays
Rapid Immunoassays
○ Are membrane-based, single-use, and disposable assays
○ Involve antigen or antibody being coupled to the membrane
Immunofluorescent assay
○ Is restricted to qualitative observations involving the use of a fluorescence microscope
Fluorescence Polarization Immunoassay (FPIA)
○ Used to determine concentrations of therapeutic drugs and hormones
○ Based on the change in polarization of fluorescent light emitted from a labeled molecule when it is bound by antibody
Chemiluminescent Immunoassays
○ Employed to follow antigen–antibody combination
○ Involve the emission of light caused by a chemical reaction, typically an oxidation reaction, producing an excited molecule that decays back to its original ground state
