Triiodothyronine - Free (T-3)
Label Mnemonic: FT3
Epic code: LAB137
Downtime form: A-1a Doctor/Provider Orders - Pathology Core and Specialty Care Nursery
Chemistry
6240 RCP
356-3527
Specimen(s):
Plasma
Collection Medium:
Plasma Separator Tube 4.5 mL
Alternate Collection Media:
Call laboratory for additional acceptable specimen collection containers.
Minimum:
3 mL whole blood in light green top or TWO Microtainer® devices
Testing Schedule:
24 hrs/day, 7 days a week, including holidays.
Turn Around Time:
1 hour (upon receipt in laboratory)
Reference Range:
Less than 1 month:  1.4-5.5 pg/mL
Less than 1 year:     2-6.9 pg/mL
1 - 5 years:        2.4-6.7 pg/mL
5 - 18 years:       2.3-5.5 pg/mL
Adults:           2.57-4.43 pg/mL

To convert results to ng/dL, multiply result x.1
To convert results to pmol/L, multiply result x 1.54
Comments:
This assay may be significantly impacted by high-dose biotin (>5 mg dose) taken within previous 12 hours. High concentrations of biotin may lead to falsely decreased results. These concentrations may be found in patients taking over-the-counter supplements with biotin content much higher than nutritional requirements for biotin. Specimens should not be collected until at least 12 hours after the last dose.
Test Limitations:
The assay is unaffected by icterus (bilirubin is less than 66 
mg/dL), hemolysis (Hb is less than 1000 mg/dL), lipemia (Intralipid is 
less than 2000 mg/dL) and biotin is less than 100 ng/mL (criterion: 
recovery within plus or minus 10% of initial value).

18 commonly used pharmaceuticals were tested in vitro. No interference 
with the assay was found.

Therapeutic concentrations of acetylsalicylic acid and furosemide lead 
to elevated FT3 values.

Autoantibodies to thyroid hormones can interfere with the assay.

The risk of interference from potential immunological interactions 
between test components and rare sera has been minimized by the 
inclusion of suitable additives. In rare cases, interference due to 
extremely high titers of antibodies to streptavidin and ruthenium can 
occur. FT3 contains additives which minimize these effects.  For 
diagnostic purposes, the FT3 findings should always be assessed in 
conjunction with the patient's medical history, clinical examination 
and other findings.
Methodology:
Electrochemiluminescence Immunoassay
CPT Code:
84481
 
See Additional Information:
Biotin Interference with Immunoassays