T4 (Thyroxine), Total Only, Serum
Use
The T4 (Thyroxine), Total Only, Serum test is useful for monitoring treatment with synthetic hormones, as synthetic T3 (triiodothyronine) will cause a low total T4 (thyroxine). It is also used to monitor the treatment of hyperthyroidism with thiouracil and other anti-thyroid drugs. Additionally, it serves as an index of thyroid function when the thyroxine-binding globulin is normal and non-thyroidal illness is not present. Measurement of total T4 gives a reliable reflection of clinical thyroid status, in the absence of protein-binding abnormalities and non-thyroidal illness.
Special Instructions
This test cannot be used in patients receiving treatment with lipid-lowering agents containing dextrothyroxine unless therapy is discontinued for 4 to 6 weeks to allow the physiological state to become reestablished prior to testing.
Limitations
Binding protein anomalies may cause values that deviate from the expected results, and pathological concentrations of binding proteins can lead to results outside the reference range, although the patient may be in a euthyroid state. In pregnancy, incomplete release of T4 from its binding proteins might result in falsely low total T4 levels, therefore total T4 should not be used as the only marker for thyroid function evaluation. The presence of human anti-mouse antibodies (HAMA) and other heterophile antibodies can interfere with this assay, as well as the presence of antibodies to streptavidin or ruthenium.
FDA ApprovedNew York Approved
Methodology
Immunoassay (ECLIA)
Biomarkers
LOINC Codes
- 83119-8
- 83119-8
Result Turnaround Time
1-3 days
Related Documents
For more information, please review the documents below
Specimen
Serum
Volume
1 mL
Minimum Volume
0.75 mL
Container
Serum gel or Red top tube, plastic vial
Collection Instructions
Centrifuge and aliquot serum into a plastic vial.
Patient Preparation
For 4 to 6 weeks before specimen collection, patient should not be taking lipid-lowering medications containing dextrothyroxine.
Causes for Rejection
Gross hemolysis
Stability Requirements
| Temperature | Period |
|---|---|
| Refrigerated | 7 days |
| Frozen | 30 days |