Thyroxine, Total T4
Also known as: T4 TOTAL
Use
Thyroxine, Total T4 measurement is critical for assessing thyroid function and diagnosing thyroid disorders. It provides essential information about the thyroid hormone levels, which are crucial for metabolic processes, growth, and development. This test helps identify both hyperthyroidism and hypothyroidism, adjusting treatment and monitoring responses to therapy. It is not recommended for routine screening but is valuable in evaluating existing thyroid dysfunction and guiding endocrinological healthcare decisions.
Special Instructions
For initial thyroid disorder screening, it is recommended to use Thyroid Stimulating Hormone (TSH) testing rather than this test. This test should be considered when specific assessment of the total T4 level is required as part of a comprehensive thyroid evaluation.
Limitations
This test cannot be used as a standalone diagnostic tool for thyroid disorders. Variability can occur due to factors such as protein-binding or medication interference. Total T4 levels can be affected by conditions unrelated to thyroid function, such as pregnancy, oral contraceptives, and systemic illnesses. Results should be interpreted in conjunction with other thyroid function tests, patient history, and clinical findings to ensure accurate diagnosis and management.
New York Approved
Methodology
Immunoassay (ECLIA)
Biomarkers
LOINC Codes
- 3026-2
Result Turnaround Time
1 day
Related Documents
For more information, please review the documents below
Specimen
Serum
Volume
1 mL
Minimum Volume
0.5 mL
Container
Serum separator tube or green (lithium heparin); also acceptable: lavender (K2EDTA or K3EDTA), or pink (K2EDTA)
Collection Instructions
Allow specimen to clot completely at room temperature. Separate serum or plasma from cells ASAP or within 2 hours of collection. Transfer to an ARUP standard transport tube.
Storage Instructions
Refrigerated transport.
Causes for Rejection
Grossly hemolyzed specimens.
Stability Requirements
| Temperature | Period |
|---|---|
| Room Temperature | 4 days |
| Refrigerated | 8 days |
| Frozen | 1 year |