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  • Test Details
  • Lab Values
  • Clinical Significance
  • Treatment Options
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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

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
Test Details
Clinical Significance

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
  • 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

Free T3 (Free Triiodothyronine or FT3)

Treatment is based on the cause of elevation/reduction.

Clinical Significance