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HelpTest Code TT3 Total T3
Additional Codes
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Cerner |
NextGen |
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Total T3 |
Total T3 |
Alternate Name(s)
TT3
Total Triiodothyronine
Methodology
Competitive Immunoassay
Patient Preparation
None
Collection Instructions
Standard phlebotomy practices.
Specimen Requirements
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Container |
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Stability |
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Rejection Criteria |
Gross Hemolysis Turbid Specimens |
Result Reporting and Reference Values
Reported in ng/dL
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Age |
Low |
High |
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0 to 2 Weeks |
31.4 |
301 |
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2 Weeks to 10 Years |
139 |
301 |
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10 to 18 Years Male |
127 |
339 |
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10 to 18 Years Female |
112 |
208 |
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18-150 Years |
97.0 |
169.0 |
Reflex Testing
None
Limitations
- Contact the Laboratory for full list of known interfering substances.
- Certain drugs and clinical conditions are known to alter T3 concentrations in vivo. For additional information, refer to one of the published summaries.
- Tate J, Ward G. Interferences in Immunoassay. Clin Biochem Rev. Vol 25: 105–120; May 2004.
- Friedman, R.B.; Young, D.S. Effects of Disease on Clinical Laboratory Tests. 4th ed. Washington, D.C.: AACC Press; 2001.
- Tryding N, Tufvesson C, Sonntag O, eds. Drug Effects in Clinical Chemistry. 7th ed. Stockholm: The National Corporation of Swedish Pharmacies, Pharmasoft AB, Swedish Society for Clinical Chemistry; 1996
- Heterophile as well as human anti-animal antibodies (most common human anti-mouse antibodies or HAMA) in serum or plasma of certain individuals are known to cause interference with immunoassays. The anti-animal antibodies may be present in blood samples from individuals regularly exposed to animals or who have received preparations of mouse monoclonal antibodies for diagnosis or therapy. Results inconsistent with clinical observations indicate the need for additional testing.
- Metabolites of the drug Diclofenac may cause inappropriately elevated results in this test. Results from patients receiving this drug should be interpreted with caution.
- Thyroid hormone autoantibodies in samples may cause interference with this test. Results that are inconsistent with clinical observations indicate the need for additional testing.
Useful For
Triiodothyronine is transported in serum primarily by thyroxine-binding globulin (TBG), approximately 99.5 % T3 is protein-bound. T3 contributes significantly to the maintenance of the euthyroid state and the total T3 concentration has a role in screening for thyroid disease in conjunction with other tests. T3 alone cannot diagnose hypothyroidism, but it may be more sensitive than thyroxine (T4) for hyperthyroidism. A fall in T3 concentrations of up to 50% is known to occur in a variety of clinical situations, including acute and chronic disease. T3 concentrations may be altered in conditions affecting the capacity of the thyroid hormone binding proteins, e.g., pregnancy, when a test for T3 or T4 uptake may be used with the total T3 result to calculate the free T3 index (FT3I) to estimate the level for metabolically active free T3.