T4, Free (1016)

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Category:

CPT Code:

84439

Test Type: Kit Based
Stability Time:

Stability

Refrigerated: 7 days  (7 days on SST gel)

Reference Range:
  • Low: <0.93 ng/dL
  • Optimal: 0.93-1.70 ng/dL
  • High: >1.70 ng/dL

Overview:

Free T4 is the amount of T4 hormone that is freely circulating in the blood.

Methodology

Chemiluminescence immunoassay

 

  • Low Free T4 levels are consistent with an underactive thyroid gland or inadequate thyroid hormone replacement.1-3
  • High Free 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.

 

Collection Details:

Collection Instructions:

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)