T3 (Triiodothyronine) Antibody

Test Code

CPT Codes

Preferred Specimen
1 mL serum

Minimum Volume
0.5 mL

Transport Container
Transport tube

Transport Temperature
Room temperature

Specimen Stability
Room temperature: 14 days
Refrigerated: 14 days
Frozen: 28 days

Reject Criteria (Eg, hemolysis? Lipemia? Thaw/Other?)
Gross hemolysis • Grossly lipemic

Immunoassay (IA)

FDA Status
This test was developed and its analytical performance characteristics have been determined by Quest Diagnostics. It has not been cleared or approved by FDA. This assay has been validated pursuant to the CLIA regulations and is used for clinical purposes.

Setup Schedule
Set up: Sun, Wed; Report available: 4-8 days

Nonthyroidal chronic diseases, nicotinic acid and nutrition may decrease results. Thyrotoxicosis may not always cause abnormal results. Binding protein variations may cause variations in results. Increases may be associated with pregnancy or oral contraceptive use.

Reference Range

Clinical Significance
This test helps identify triiodothyronine (T3) thyroid hormone autoantibodies (THAAbs), which may interfere with T3 immunoassays in individuals with discordant serum T3 levels [1].

THAAbs may present in healthy individuals but are more common in patients with autoimmune thyroid diseases. THAAbs may affect both 1-step and 2-step immunoassays; the interference may be transient or persist for years. T3 THAAbs interfere with T3 measurements by competing with T3 antibodies used in the T3 immunoassays. When the serum T3 level is discordant with clinical manifestations or other test results (eg, elevated T3 levels with normal or elevated thyroid stimulating hormone [TSH] levels), this test may be used to determine whether T3 THAAbs are the cause of discordance [1].

Other methods of screening for interference by T3 THAAbs are polyethylene glycol precipitation and comparison against equilibrium dialysis. Anomalous T3 levels may also be caused by a range of interfering substances, such as biotin, heterophilic antibodies, and antibodies to streptavidin and ruthenium [1].

Other conditions that may result in elevated free thyroxine and/or free T3 levels without suppressed TSH levels include thyroxine replacement therapy, familial dysalbuminemic hyperthyroxinemia, certain drugs (eg, amiodarone and heparin), nonthyroidal illness, neonatal period, TSH-secreting pituitary adenoma, resistance to thyroid hormone, and disorders of thyroid hormone transport or metabolism [2].

The results of this test should be interpreted in the context of pertinent clinical and family history and physical examination findings.

1. Favresse J, et al. Endocr Rev. 2018;39(5):830-850.
2. Gurnell M, et al. Clin Endocrinol (Oxf). 2011;74(6):673-678.

Performing Laboratory
Quest Diagnostics Nichols Institute-San Juan Capistrano, CA
33608 Ortega Highway
San Juan Capistrano, CA 92675-2042

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.