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This bioassay compares the cyclic adenosine monophosphate (cAMP) production of thyroid-stimulating hormone (TSH)-responsive cells upon exposure to patient serum with that obtained in the same cells after exposure to normal control serum.
The assay uses Chinese hamster ovary cells that have been permanently transfected with the human thyroid-stimulating hormone receptor (TSHR) and a luciferase expression construct under the control of a cAMP responsive promoter. Luciferase transcription in these cells is proportional to the concentration of intracellular cAMP.
The cells are grown to near-confluence. An aliquot of cells is then incubated with each diluted patient serum. Cells are lysed at the end of incubation, luciferase substrate is added and chemiluminesence is measured in a luminometer. The ratio of the light-units produced in the cell-lysate exposed to patient serum divided by a control cell-lysate light-signal is the TSI index.(Preissner CM, Wolhuter PJ, Sistrunk JW, et al: Comparison of thyrotropin-receptor antibodies measured by four commercially available methods with a bioassay that uses Fisher-rat thyroid cells. Clin Chem 2003;49:1402-1404; Package insert: Thyroid Stimulating Immunoglobulin Assay. Diagnostic Hybrids)
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