Test Code 1017
Test Details
Free T3 (Free Triiodothyronine or FT3)
Free T3 is the amount of T3 hormone that is freely circulating in the blood.
Methodology
Chemiluminescence immunoassay
Patient Preparation
None
Preferred Specimen
1.0 mL serum collected in a serum separator tube (SST / Tiger Top)
Alternate Specimen
1.0 mL plasma in an EDTA plasma separator tube (Pearl Top)
Transport Temperature
Refrigerated (ship on frozen cold packs)
Stability
Refrigerated: 7 days (7 days on SST gel)
Lab Values
Free T3 (Free Triiodothyronine or FT3)
- Low: <2.0 pg/mL
- Optimal: 2.0-4.4 pg/mL
- High: >4.4 pg/mL
Clinical Significance
Free T3 (Free Triiodothyronine or FT3)
- Low Free T3 levels are consistent with hypothyroidism or inadequate thyroid hormone replacement.1-3
- High Free T3 levels are consistent with either hyperthyroidism 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
Free T3 (Free Triiodothyronine or FT3)
Treatment is based on the cause of elevation/reduction.
