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Lab Dept:
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Chemistry
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Test Name:
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FREE TRIIODOTHYRONINE (FT3)
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General Information
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Lab Order Codes:
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FT3
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Synonyms:
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Free T3; FT3
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CPT Codes:
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84481 – Triiodothyronine T3; free
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Test Includes:
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Free triiodothyronine concentration reported in pg/mL.
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Logistics
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Test Indications:
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Free Triiodothyronine (T3) is a second or third level test of thyroid function. It provides further confirmation of hyperthyroidism, supplementing the tetraiodothyronine (T4), sensitive thyrotropin (sTSH), and total T3 assays. Monitoring thyroid hormone replacement.
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Lab Testing Sections:
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Chemistry - Sendouts
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Referred to:
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Mayo Medical Laboratories (MML Test# 9404)
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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
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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 tube
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Draw Volume:
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1.8 mL (Minimum: 1.5 mL) blood
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Processed Volume:
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0.6 mL (Minimum: 0.5 mL) serum
Note: Submission of the minimum volume does not allow for repeat analysis and may results in QNS (quantity not sufficient) test results.
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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 into a screw-capped round bottom plastic vial. Store and ship at refrigerated temperatures. Forward promptly.
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Patient Preparation:
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None
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Sample Rejection:
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Gross hemolysis; warm specimens; mislabeled or unlabeled specimen
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Interpretive
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Reference Range:
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Age
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Range
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<1 year:
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Reference values have not been established for patients that are less than 12 months of age.
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≥1 year:
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2.0 – 3.5 pg/mL
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Critical Values:
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N/A
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Limitations:
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FT3 is not a sensitive test for hypothyroidism.
Some patients who have been exposed to animal antigens, either in the environment or as part of treatment or imaging procedures, may have circulating anti-animal antibodies present. These anti-bodies may interfere with the assay reagents to produce unreliable results.
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Methodology:
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Immunoenzymatic Assay
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References:
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Mayo Medical Laboratories April 2011
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