Triiodothyronine (T-3)
Label Mnemonic: TT3
Epic Lab Code: LAB136
Downtime Form: A-1a Doctor/Provider Orders - Pathology Core and Specialty Care Nursery
6240 RCP
Collection Medium:
Plasma Separator Tube 4.5 mL
Alternate Collection Media:
Call laboratory for additional acceptable specimen collection containers.
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:
AGE MALES/FEMALES 0 - 3 days 0.6-3.0 ng/mL 4 days - 1 year 0.9-2.6 ng/mL 1 day - 6 years 0.9-2.4 ng/mL 7 - 11 years 0.9-2.3 ng/mL 12 - 18 years 1.0-2.1 ng/mL Adults 0.8-2.0 ng/mL
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 less than 35 mg/dL), hemolysis (Hb less than 2000 mg/dL), lipemia (triglycerides less than 1800 mg/dL) and biotin is less than 10 ng/mL (criterion: recovery within plus or minus 10% of initial value). No interference was observed from rheumatoid factor (up to 1500 U/mL) and samples from dialysis patients. Twenty-six commonly used pharmaceuticals were tested in vitro. No interference with the assay was found. Therapy with amiodarone can lead to abnormal thyroid hormone tests. Phenytoin, phenylbutazone and salicylates cause release of T3 from the binding proteins, thus leading to a reduction in the total T3 hormone level at normal fT3 levels. Auto-antibodies to thyroid hormones can interfere with the test. Pathological concentrations of binding proteins (TBG, albumin) can lead to total T3 values outside the normal range being found despite a euthyroid metabolic state (e.g. in NTI-patients, pregnancy, use of oral contraceptives). In such cases, determination of free T4 and/or free T3 may be indicated. The risk of interference from potential immunological interactions between test components and rare sera has been minimized by the inclusion of additives. For diagnostic purposes, the T3 findings should always be assessed in conjunction with the patient's medical history, clinical examination and other findings.
Electrochemiluminescence Immunoassay
CPT Code:
See Additional Information:
Biotin Interference with Immunoassays