Triiodothyronine (T3)
Also known as: T3, Total
Use
Thyroid function which is particularly useful in the diagnosis of T3 thyrotoxicosis, in which T3 is increased and T4 is within normal limits. T3 toxicosis is occasionally found in Graves' disease. It occurs with a single toxic nodule, multinodular thyrotoxicosis, and following treatment with T3 (Cytomel®).2 It is increased in and occasionally helpful for confirmation of diagnosis of conventional hyperthyroidism, in which commonly both T3 and T4 levels are increased. T3 is needed in patients with clinical evidence for hyperthyroidism, in whom the usual thyroid profile is normal or borderline.
Special Instructions
This test may exhibit interference if the sample is collected from individuals consuming high doses of biotin (vitamin B7, H, or coenzyme R). It's recommended to halt biotin consumption at least 72 hours before sample collection.
Limitations
T3 levels can be decreased in cases of non-thyroidal chronic illnesses and impacted by nutritional status. It is not suitable for hypothyroidism evaluation and may present as normal in thyroxine thyrotoxicosis. T3 variations could arise from changes in TBG and binding proteins, affected by pregnancy or contraceptive usage. Continued fasting can also cause a decrease in T3 and TSH levels.
Methodology
Immunoassay (ECLIA)
Biomarkers
LOINC Codes
- 3053-6
- 3053-6
Result Turnaround Time
1 day
Related Documents
For more information, please review the documents below
Specimen
Serum
Volume
1 mL
Minimum Volume
0.7 mL
Container
Red-top tube, gel-barrier tube, or green-top (lithium heparin) tube. Do not use oxalate, EDTA, or citrate plasma.
Collection Instructions
If a red-top tube or plasma is used, transfer separated serum or plasma to a plastic transport tube.
Patient Preparation
Patients should stop biotin consumption at least 72 hours prior to sample collection.
Storage Instructions
Room temperature
Causes for Rejection
Citrate plasma specimen; improper labeling
Stability Requirements
| Temperature | Period |
|---|---|
| Room Temperature | 14 days |
| Refrigerated | 14 days |
| Frozen | 14 days |