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  • Test Details
  • Lab Values
  • Clinical Significance
  • Treatment Options
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Explore this test

Test Code 1015

Test Details

Total T4 (Thyroxine or T4)

Total T4 (thyroxine) is a hormone produced by the thyroid gland and is converted in the body’s tissue to the major active thyroid hormone T3.

Methodology

Chemiluminescence immunoassay

Patient Preparation

None

Preferred Specimen

1.0 mL serum collected in a serum separator tube (SST / Tiger Top)

Alternate Specimen

None

Transport Temperature

Refrigerated (ship on frozen cold packs)

Stability

Refrigerated: 8 days

Lab Values

Lab Values

Total T4 (Thyroxine or T4)

  • Low: <4.5 µg/dL
  • Optimal: 4.5-11.7 µg/dL
  • High : >11.7 µg/dL
Test Details
Clinical Significance

Clinical Significance

Total T4 (Thyroxine or T4)

  • Low Total T4 levels are consistent with an underactive thyroid gland or inadequate thyroid hormone replacement.1-3
  • High Total T4 levels are consistent with either an overactive thyroid gland or excess thyroid hormone replacement.1-3
  • High doses of biotin (> 5 mg/day) may interfere with assay results. Patient assumed to be refraining from biotin supplementation for at least 3 days prior to blood draw.

References:

  1. Goodman N, Cobin RH. Reproductive disorders. In: Camacho PM, Gharib H, Sizemore GW, eds. Evidence-Based Endocrinology. 3rd ed. Philadelphia, PA: Lippincott Williams & Wilkins. 2012:190-228.
  2. Castro MR, Gharib H. Thyroid disorders. In: Camacho PM, Gharib H, Sizemore GW, eds. Evidence-Based Endocrinology. 3rd ed. Philadelphia, PA: Lippincott Williams & Wilkins. 2012:43-80.
  3. Garber JR, Cobin RH, Gharib H, et al. Clinical practice guidelines for hypothyroidism in adults: cosponsored by the American Association of Clinical Endocrinologists and the American Thyroid Association. Endocr Pract. 2012;18(6):988-1028.
Lab Values
Treatment Options

Treatment Options

Total T4 (Thyroxine or T4)

Treatment is based on the cause of elevation/reduction.

Clinical Significance