Order Code: C144
ABN Requirement: No
Synonyms: Total T3; T3
Specimen: Serum
Volume: 0.5 mL
Minimum Volume: 0.2 mL
Container: Gel-barrier tube (SST, Tiger Top)
Collection:
- Collect and label sample according to standard protocols.
- Gently invert tube 5 times immediately after draw. DO NOT SHAKE.
- Allow blood to clot 30 minutes.
- Centrifuge for 10 minutes.
Transport: Store serum at 2°C to 8°C after collection and ship the same day per packaging instructions provided with the Cleveland HeartLab shipping box.
Stability:
Ambient (15-25°C): 8 days
Refrigerated (2-8°C): 14 days
Frozen (-20°C): 12 months
Deep Frozen (-70°C): 12 months
Causes of Rejection: Samples which are heat-inactivated; specimens other than serum; improper labeling; samples not stored properly; samples older than stability limits
Methodology: Electrochemiluminescence Immunoassay (ECLIA)
Turn Around Time: 1 to 5 days
Reference Range:
| Age | ng/dL |
| 0-2 weeks | 100-740 |
| 3-4 weeks | 100-260 |
| 5 weeks-12 months | 94-170 |
| 13-20 months | 100-260 |
| ≥21 months | 80-200 |
Intended Use: A doctor may order a total triiodothyronine test for the evaluation of an abnormal TSH test result to distinguish between different causes of hyper- and hypothyroidism and to confirm the diagnosis of T3-thyroidosis. The total triiodothyronine test is also used for the evaluation of thyroid function in patients with TBG alterations, to evaluate individuals with goiter and to aid in the diagnosis of infertility in women.
Limitations: Therapy with amiodarone can lead to depressed T3 values. Phenytoin, phenylbutazone, and salicylates cause release of T3 from the binding protein, thus leading to a reduction of the total T3 hormone at normal fT3 levels. Autoantibodies to thyroid hormones can interfere with the assay. Binding protein anomalies seen with FDH (familial dysalbuminemic hyperthyroxinemia), for example, may cause values which, while characteristic of the condition, deviate from the expected results. 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, fT3 or fT4 determination is indicated. In rare cases, interference due to extremely high titers of antibodies to analyte-specific antibodies, streptavidin or ruthenium can occur.
The CPT codes provided 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 payer being billed.