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Free Triiodothyronine (FT3)

FT₃, Free T₃, T₃, Free

Test Codes

EPIC: LAB5121, Beaker: FRT3

Department

Chemistry

Specimen Collection Criteria

Collect: One Gold-top SST tube. (Minimum Whole Blood: 4.0 mL)

Contact the Laboratory for the acceptability of other tube types.
See Minimum Pediatric Specimen Requirements for Microtainer^® collection.

Note: Patient Preparation (Farmington Hills ONLY): Twenty-four (24) hours before this test, the patient should not take multivitamins or dietary supplements containing biotin (vitamin B7) which is commonly found in hair, skin and nail supplements and multivitamins.

Physician Office/Draw Specimen Preparation

Let SST specimens clot for 30-60 minutes then immediately centrifuge to separate serum from cells. Refrigerate (2-8°C or 36-46°F) the centrifuged SST tube within two hours of collection. (Minimum: 0.5 mL)

Preparation for Courier Transport

Transport: Centrifuged SST tube, refrigerated (2-8°C or 36-46°F). (Minimum: 0.5 mL)

Rejection Criteria

• Grossly hemolyzed specimens.
• Red-top tubes with serum not separated from cells within two hours of collection.

In-Lab Processing

Let SST specimens clot 30-60 minutes. Centrifuge SST tubes or Microtainers^® to separate serum from cells. Deliver immediately to the appropriate testing station.

Storage

Specimen Stability for Testing:

Centrifuged SST Tubes and Microtainers^® with Separator Gel
Room Temperature (20-26°C or 68-78.8°F): 2-4 hours
Refrigerated (2-8°C or 36-46°F): 7 days
Frozen (-20°C/-4°F or below): Unacceptable

Red-top Tubes and Microtainers^® without Separator Gel
Room Temperature (20-25°C or 68-77°F): 2-4 hours
Refrigerated (2-8°C or 36-46°F): Unacceptable
Frozen (-20°C/-4°F or below): Unacceptable

Serum Specimens (Pour-Overs)
Room Temperature (20-26°C or 68-78.8°F): 2-4 hours
Refrigerated (2-8°C or 36-46°F): 7 days
Frozen (-20°C/-4°F or below): 7 days

Specimen Storage in Department Prior to Disposal:

Refrigerated (2-8°C or 36-46°F): 7 days

Laboratory

Royal Oak Automated Chemistry Laboratory
Troy Chemistry Laboratory

Performed

Sunday – Saturday, 24 hours a day.
Results available within 24 hours of receipt in the Chemistry Laboratory.

Reference Range

1.7 - 3.7 pg/mL.

Test Methodology

Chemiluminescence Immunoassay.

Interpretation

Elevated FT₃ values are associated with thyrotoxicosis or excess thyroid hormone replacement.

Clinical Utility

Clinically, the FT₃ measurement is a second or third level test of thyroid function. It is useful for evaluating the biochemical status of clinically euthyroid patients who have an altered distribution of binding proteins, such as pregnant patients and patients with dysalbuminemia. It also provides a further confirmatory test for hyperthyroidism to supplement the FT₄ and sensitive thyrotropin assays. Some investigators recommend the FT₃ assay for monitoring thyroid replacement therapy, although its clinical role is not precisely defined.

CPT Codes

84481

Contacts

Last Updated

10/29/2023