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Lab Dept:
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Chemistry
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Test Name:
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T4 (THYROXINE) TOTAL, SERUM
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General Information
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Lab Order Codes:
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T4
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Synonyms:
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T4 Total, Thyroxine
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CPT Codes:
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84436 – Thyroxine; total
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Test Includes:
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Thyroxine concentration reported in ug/dL.
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Logistics
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Test Indications:
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Thyroxine is a hormone synthesized and secreted by the thyroid gland and plays an important role in regulating metabolism. T4 is secreted into the circulation in response to the pituitary hormone, TSH. T4 measurements provide information on thyroid function.
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Lab Testing Sections:
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Chemistry (all specimens tested on the St. Paul campus)
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Phone Numbers:
Minneapolis:
Saint Paul:
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612-813-6280
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651-220-6550
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Test Availability:
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Daily, 24 hours
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Turnaround Time:
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1 – 3 days, test performed Monday – Friday.
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Special Instructions:
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N/A
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Specimen
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Specimen Type:
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Blood
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Container:
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Red top (plain, no gel) tube
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Draw Volume:
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1.5 mL (Minimum: 0.6 mL) blood
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Processed Volume:
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0.5 mL (Minimum: 0.2 mL) serum
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Collection:
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Routine venipuncture
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Special Processing:
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Lab Staff: Centrifuge specimen, remove serum aliquot into a plastic sample cup. Store at refrigerated temperatures.
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Patient Preparation:
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None
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Sample Rejection:
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Mislabeled or unlabeled specimen; specimens other than serum; gross hemolysis
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Interpretive
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Reference Range:
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Age:
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Range (ug/dL):
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0 days:
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8.3 – 19.0 ug/dL
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1 – 6 days:
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10.0 – 20.0 ug/dL
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7 – 30 days:
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7.5 – 15.4 ug/dL
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1 month – 1 year:
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5.2 – 15.9 ug/dL
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> 1 year:
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4.6 – 11.2 ug/dL
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Critical Values:
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N/A
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Limitations:
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Heterophile antibodies may interfere with immunoassay testing. The drug phenytoin may interfere with the T4 assay due to competition for TBG binding sites.
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Methodology:
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Competitive Immunoassay/Chemiluminescence
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References:
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DPC End User Procedure Manual Disk #0408111 (2005)
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Siemens Immulite Total T4 product insert (07/29/2008) PIL2KT4-21
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National Committee for Clinical Laboratory Standards (NCCLS) (2002) Clinical Laboratory Technical Procedure Manuals; Approved Guideline-Fourth Edition GP2-A4
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Biorad Immunoassay Plus Control Product Insert
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Burtis, CA, Ashwood, ER, Bruns, DE, editors (2006) Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. 4th Edition, Philadelphia: W.B. Saunders, 2006.
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Jacobs and DeMott Laboratory Test handbook (2001) 5th Edition, Lexi-comp Inc
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