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Test Code T3FRE T3, Free

Additional Codes

Epic: LAB137

Specimen Required

Collection Container/Type

Preferred: Serum gel

Acceptable: Green top (Lithium heparin)
Submission Container/Tube: Plastic vial
Specimen Volume: 3.0 mL
Collection Instructions: Centrifuge and separate cells after clot formation and within 4 hours of collection.  Remove serum if testing will be delayed more than 24 hours.

Specimen Minimum Volume

0.3 mL

Specimen Stability

Room Temperature: Unacceptable
Refrigerated (on gel): 24 hours
Refrigerated (off gel): 6 days
Frozen: >6 days

Reference Range

1.71 pg/mL - 3.71 pg/mL

Rejection Due To

Samples stored on gel >24 hours, unlabeled, mislabeled, wrong tube type, hemolyzed, QNS, exceeds specimen stability requirements.

Report Available

Same day

Clinical Significance

Triiodothyronine (T3) is a thyroid hormone with a half-life in serum of 1.5 days.  T3 circulates in the blood as an equilibrium mixture of free and protein bound hormone. T3 is bound to thyroxine binding globulin (TGB), prealbumin and albumin.  The binding of T3 by these proteins is such that only 0.2 – 0.4% of the total T3 is present in solution as unbound or free T3.  This free T3 fraction represents the physiologically biologically active hormone.

Method Name

Chemiluminescent microparticle immunoassay (CMIA)


For diagnostic purposes, results should be used in conjunction with other data: symptoms, results of other thyroid tests, clinical impressions, etc.
The ARCHITECT Free T3 assay is designed to have a mean potential interference from hemoglobin, bilirubin, triglycerides, and protein of <10% at : 
Hemoglobin ≤ 500 mg/dL
Bilirubin ≤20 mg/dL
Triglycerides ≤ 2000 mg/dL
Protein ≤ 12 g/dL 



Day(s) Performed