Triiodothyronine (T3), Free

Cleveland Heartlab T, Test, Thyroid Function

CPT Code: 84481
Order Code: C143
ABN Requirement:  No
Synonyms: Free T3; Unbound T3; FT3
Specimen: Serum
Volume: 0.5 mL
Minimum Volume: 0.2 mL
Container: Gel-barrier tube (SST, Tiger Top)


  1. Collect and label sample according to standard protocols.
  2. Gently invert tube 5 times immediately after draw. DO NOT SHAKE.
  3. Allow blood to clot 30 minutes.
  4. Centrifuge for 10 minutes.

Special Instructions: Samples should not be taken from patients receiving therapy with high biotin doses (>5 mg/day) until at least 8 hours following the last dose.

Transport: Store serum at 2°C to 8°C after collection and ship the same day per packaging instructions provided with the Cleveland HeartLab shipping box.


Ambient (15-25°C): 5 days
Refrigerated (2-8°C): 7 days
Frozen (-20°C): 30 days
Deep Frozen (-70°C): 30 days

Causes of Rejection: Samples which are heat-inactivated; samples stabilized with azide; specimens other than serum; improper labeling; samples not stored properly; samples older than stability limits

Methodology: Electrochemiluminescence Immunoassay (ECLIA)

Turn Around Time: 1 to 3 days

Reference Range:

Age pg/mL
0-12 months 2.9-6.8
13 months-6 years 2.5-5.3
7-12 years 2.5-5.6
13-17 years 2.4-5.0
≥18 years 2.0-4.4


Intended Use: The free triiodothyronine test is used for the evaluation of thyroid function, hyperthyroidism and T3-thyrotoxicosis, and to monitor individuals with a known thyroid disorder.

Limitations: Furosemide and Levothyroxine caused increased FT3 results at the daily therapeutic dosage level. Any influence that might affect the binding behavior of the binding proteins can alter the result of the FT3 tests (e.g. drugs, Non-Thyroid-Illness or NTI, or patients suffering from Familial Dysalbuminemic Hyperthyroxinemia or FDH). Autoantibodies to thyroid hormones can interfere with the assay. In rare cases, interference due to extremely high titers of antibodies to analyte-specific antibodies, streptavidin or ruthenium can occur.

The CPT codes provided are based on AMA guidelines and are for informational purposes only. CPT coding is the sole responsibility of the billing party. Please direct any questions regarding coding to the payer being billed.