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Test Code Billings Clinic: 8995 T3 (Triiodothyronine), Free, Plasma or Serum

Important Note

Although this assay is FDA Approved for other patient populations the assay performance characteristics have not been established for neonates.

Performing Laboratory

Billings Clinic Laboratory: Chemistry

Useful For

  • Free triiodothyronine (T3) is a second- or third-level test of thyroid function; it provides further confirmation of hyperthyroidism, supplementing the tetraiodothyronine (T4), sensitive thyrotropin (sTSH), and total T3 assays.
  • Evaluating clinically euthyroid patients who have an altered distribution of binding proteins
  • Monitoring thyroid hormone replacement therapy

Methodology

Direct Chemiluminescence

Specimen Requirements

Submit only 1 of the following specimens:

Serum or plasma should be physically separated from cells as soon as possible with a maximum limit of two hours from the time of collection.

 

Plasma

  • Draw blood in a green-top (lithium heparin) tube(s).
  • Spin down and send 1.0 mL of heparinized plasma frozen.

 

Serum

  • Draw blood in a plain, red-top tube(s) or a serum gel tube(s).
  • Spin down and send 1.0 mL of serum frozen

Storage/Stability

Specimen Type Temperature Time
Plasma, Serum Refrigerated 2 days
  Frozen (preferred) 1 month
  Ambient 8 hours

 

Reject Due To

  • Gross hemolysis
  • Specimens with apparent contamination
  • Specimens stored at room temperature greater than 8 hours
  • Samples frozen and thawed more than once

Reference Values

Males:

0 - 1 year:  3.34 - 4.88 pg/mL

1 - 12 years:  3.31 - 4.88 pg/mL

12 - 20 years:  2.91 - 4.53 pg/mL

> 20 years:  2.18 - 3.98 pg/mL

 

Females:

0 - 1 year:  2.18 - 3.98 pg/mL

1 - 12 years:  3.31 - 4.53 pg/mL

12 - 20 years:  2.91 - 4.53 pg/mL

> 20 years:  2.18 - 3.98 pg/mL

 

Day(s) Test Set Up

Daily

Test Classification and CPT Coding

84481 - Free T3

LOINC Code Information

Reporting Name LOINC Code
Free T3 3051-0