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
Total T4 (Thyroxine or T4)
- Low: <4.5 µg/dL
- Optimal: 4.5-11.7 µg/dL
- High : >11.7 µg/dL
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
- These assays no longer show biotin interference in serum concentrations up to 1200 ng/mL.
References:
- 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.
- 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.
- 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.
Treatment Options
Total T4 (Thyroxine or T4)
Treatment is based on the cause of elevation/reduction.
