T4 (Thyroxine), Total
Use
Used to help diagnose hypothyroidism and hyperthyroidism, by measuring the total thyroxine (T4) in the blood, which reflects both free and protein-bound hormone concentrations. The Free T4 Index (T7) may also be calculated if T3 Uptake (test code 861) is ordered concurrently.
Special Instructions
Free T4 Index (T7) will only be calculated and reported if test code 861 (T3 Uptake) is ordered as well.
Limitations
Nonthyroidal chronic diseases, nicotinic acid and nutritional factors may decrease results. Thyrotoxicosis may not always cause abnormal results. Variations in binding proteins may cause result variability. Increases may be associated with pregnancy or oral contraceptive use.
Methodology
Immunoassay
Biomarkers
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 (SST)
Causes for Rejection
Hemolysis; specimens exceeding stability; specimens other than serum; unlabeled or improperly labeled specimens
Stability Requirements
| Temperature | Period |
|---|---|
| Room Temperature | 7 days |
| Refrigerated | 7 days |
| Frozen | 28 days |
Other tests from different labs that may be relevant