Test ID: CGAK
Chromogranin A, Serum
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Chromogranin A (CGA) is measured in a homogeneous automated immunofluorescent assay. This assay uses technology based on a variant of Forster resonance energy transfer, called time-resolved amplified cryptate emission (TRACE). A mouse monoclonal antibody against CGA is labeled with europium cryptate (TRACE donor) and a second mouse monoclonal antibody against CGA is labeled with XL665 (TRACE acceptor). CGA is sandwiched between the 2 antibodies, bringing them into close proximity. When the antigen-antibody complex is excited with a nitrogen laser at 337 nm, some fluorescent energy is emitted at 620 nm and the rest is transferred by nonradiative dipole-dipole coupling to XL665. This energy is then emitted as fluorescence at 665 nm. A ratio of the energy emitted at 665 nm to that emitted at 620 nm (internal reference) is calculated for each sample. Signal intensity is proportional to the number of antigen-antibody complexes formed, and therefore to antigen concentration.(Unpublished Mayo method)
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