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Test Code 340 Total T4 (Thyroxine)

Important Note

Human anti-mouse antibodies (hama) may be present in samples from patients who have received immunotherapy or diagnostic procedures utilizing monoclonal antibodies or in individuals who have been regularly exposed to animals. Additionally, other heterophile antibodies, such as human anti-goat antibodies may be present in patient samples. Manufacturers formulate assays to minimize the effects of these antibodies; however careful evaluation of patient results must be done when patients are known to have such antibodies.

Additional Codes

ALAB: T4T

PowerChart: T4 (Thyroxine) Total

MA Cerner: T4

Test Method

Competitive Binding Immunoenzymatic Assay; Beckman Access DXI, Standardized to the ID-GCMS International Reference Method

Specimen Requirement

0.5 mL serum or plasma is required.

Additional Specimen Collection Information

Collect blood in a lithium heparin, green-top or red-top tube. PST and SST (gel tubes) are acceptable. Serum or plasma should be separated from contact with the cells within 2 hours of collection. Specimens not centrifuged within 4 hours of collection may be rejected. Refrigerate the specimen if unable to assay within 8 hours of collection.

Performance

Testing is performed Monday through Sunday.

Routine: Typically completed within 4 hours after the specimen arrives at the testing site.

STAT: Typically completed within 1 hour after the specimen arrives at the testing site.

Reference Values

0-3 Days: 11.8-22.6 mcg/dL

4 Days-2 Weeks: 9.8-16.6 mcg/dL

2 Weeks-4 Months: 7.2-14.4 mcg/dL

4 Months-1 Year: 7.8-16.5 mcg/dL

1-6 Years: 5.5-13.5 mcg/dL

>6 Years: 5.0-12.0 mcg/dL

CPT Code Information

84436 Chemistry: Thyroxine; total

NCD Frequency Limitations: Testing may be covered up to two times a year in clinically stable patients; more frequent testing may be reasonable and necessary for patients whose thyroid therapy has been altered or in whom symptoms or signs of hyper or hypothyroidism are noted.

Useful For

Monitoring treatment with synthetic hormones (synthetic triiodothyronine will cause a low total thyroxine: T4)

Monitoring treatment of hyperthyroidism with thiouracil and other antithyroid drugs

LOINC Code Information

3026-2 Thyroxine (T4) [Mass/Volume] In Serum Or Plasma