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For Mayo Clinic patients, any visibly blood-tinged samples are spun in a clinical centrifuge, and the supernatant is used for testing. If there is no visible blood contamination, the sample is used directly. Mayo Medical Laboratories specimens should be evaluated for hemolysis before submission.
The saline needle-wash specimen is analyzed with the Beckman Access thyroglobulin (Tg) assay, a simultaneous 1-step immunoenzymatic (sandwich) assay performed on the Beckman Coulter UniCel DxI 800. A sample is added to a reaction vessel along with a biotinylated mixture of 4 mouse monoclonal anti-Tg antibodies, streptavidin-coated paramagnetic particles, and mouse monoclonal anti-Tg antibody-alkaline phosphatase conjugate. The biotinylated antibodies and the sample Tg bind to the solid phase, while the conjugate antibody reacts with a different antigenic site on the Tg molecule. After incubation in a reaction vessel, materials bound to the solid phase are held in a magnetic field, while unbound materials are washed away. The chemiluminescent substrate Lumi-Phos530 is added to the vessel and light generated by the reaction is measured with a luminometer. Light production is directly proportional to the concentration of Tg in the sample. The amount of analyte in the sample is determined from a stored, multipoint calibration curve.(Instruction manual: Access Thyroglobulin Assay. Beckman Coulter, Inc., Fullerton, CA, 2010)
For all samples with Tg concentrations >1.0 ng/mL, a dilution series is performed. A linear dilution excludes hooking and most major interferences. Samples that contain Tg < or =1.0 ng/mL are spiked with exogenous Tg to identify possible interferences that may cause a false-low result.
Monday through Friday; 6 a.m.-12 a.m., Saturday; 6:30 a.m.-5 p.m.