Test Details
Methodology
Electrochemiluminescence immunoassay (ECLIA)
Result Turnaround Time
Within 1 day
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.
Reported to be normal to slightly increased with familial dysalbuminemic hyperthyroxinemia.
Recommended for patients with supraventricular tachycardia, for patients with fatigue and weight loss not otherwise explained, or for those with proximal myopathy and in whom T4 levels are not elevated.3
Special Instructions
This test may exhibit interference when sample is collected from a person who is consuming a supplement with a high dose of biotin (also termed as vitamin B7 or B8, vitamin H, or coenzyme R). It is recommended to ask all patients who may be indicated for this test about biotin supplementation. Patients should be cautioned to stop biotin consumption at least 72 hours prior to the collection of a sample.
Specimen Requirements
Limitations
T3 is decreased with nonthyroidal chronic diseases and influenced by the state of nutrition. It is not helpful for evaluation of hypothyroidism. It may be normal with thyrotoxicosis (thyroxine thyrotoxicosis).4
Variations in TBG and other binding proteins can affect T3. Such increases may be found with use of oral contraceptives, pregnancy, and other binding protein abnormalities. Fasting causes T3 and TSH to decrease.5
References
Custom Additional Information
Increased T3 often occurs in hyperthyroidism, but in approximately 5% of cases only T3 is elevated, “T3 toxicosis.” Do not confuse T3 with T3 uptake; these are two different tests. The latter is done very commonly as part of the usual thyroid profile. Less than 1% of T3 is unbound.
Specimen
Serum (preferred) or plasma
Volume
1 mL
Minimum Volume
0.7 mL (Note: This volume does not allow for repeat testing.)
Container
Red-top tube, gel-barrier tube, or green-top (lithium heparin) tube. Do not use oxalate, EDTA, or citrate plasma.
Storage Instructions
Room temperature
Causes for Rejection
Citrate plasma specimen; improper labeling
Collection Instructions
If a red-top tube or plasma is used, transfer separated serum or plasma to a plastic transport tube.
Stability Requirements
Temperature | Period |
|---|---|
Room temperature | 14 days |
Refrigerated | 14 days |
Frozen | 14 days |
Freeze/thaw cycles | Stable x3 |
Reference Range
See table.1
Age | Range (ng/dL) |
|---|---|
0 to 3 d | 96−292 |
4 to 30 d | 62−243 |
31 d to 12 m | 81−281 |
13 m to 5 y | 83−252 |
6 to 10 y | 92−219 |
>10 y | 71−180 |
Footnotes
LOINC® Map
| Order Code | Order Code Name | Order Loinc | Result Code | Result Code Name | UofM | Result LOINC |
|---|---|---|---|---|---|---|
| 002188 | Triiodothyronine (T3) | 3053-6 | 002188 | Triiodothyronine (T3) | ng/dL | 3053-6 |
| Order Code | 002188 | |||||
| Order Code Name | Triiodothyronine (T3) | |||||
| Order Loinc | 3053-6 | |||||
| Result Code | 002188 | |||||
| Result Code Name | Triiodothyronine (T3) | |||||
| UofM | ng/dL | |||||
| Result LOINC | 3053-6 |