T4, Total

Test Code

Alias/See Also

Epic: LAB126

Tetraiodothyronine
Thyroxine, Total
Thyroxine (T4)

Preferred Specimen

Specimen Type: Serum
Collection Container: Serum gel
Specimen Volume: 3 mL

Minimum Volume

0.3 mL

Other Acceptable Specimens

Specimen Type: Plasma
Collection Container: Green top (Lithium heparin)

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.

Transport Container

Plastic vial

Specimen Stability

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

Reject Criteria (Eg, hemolysis? Lipemia? Thaw/Other?)

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

Methodology

Chemiluminescent microparticle immunoassay (CMIA)

Setup Schedule

Daily

Report Available

Same day

Limitations

The ARCHITECT Total T4 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 ≤ 3000 mg/dL
Protein ≥ 4.5 and ≤ 12 g/dL

Reference Range

4.87 - 11.72 µg/dL

Clinical Significance

Thyroxine (T4) is an iodine-containing hormone and is secreted by the thyroid gland. T4 and its associate thyroid hormone T3 are responsible for regulating diverse biochemical processes throughout the body. T4 is 99.9% bound to serum thyroxine binding globulin. Less than 0.05% of the total circulating T4 is unbound and therefore biologically active. Elevated T4 values are seen in patient with overt hyperthyroidism, while T4 levels are generally depressed in patient with hypothyroidism.

Performing Laboratory

Inova Laboratories

2832 Juniper Street

Fairfax, VA 22031

Last Updated: March 9, 2023
Last Review: N. Wolford, March 9, 2023

The CPT Codes provided in this document 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 payor being billed. Any Profile/panel component may be ordered separately. Reflex tests are performed at an additional charge.