Synonyms
- Free T3
- T3, Free
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.
Expected Turnaround Time
1 - 2 days
Turnaround time is defined as the usual number of days from the date of pickup of a specimen for testing to when the result is released to the ordering provider. In some cases, additional time should be allowed for additional confirmatory or additional reflex tests. Testing schedules may vary.
Related Information
Related Documents
For more information, please view the literature below.
Specimen Requirements
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.
Collection
If a red-top tube or plasma is used, transfer separated serum or plasma to a plastic transport tube.
Storage Instructions
Room temperature
Stability Requirements
Temperature | Period |
|---|---|
Room temperature | 14 days |
Refrigerated | 14 days |
Frozen | 14 days |
Freeze/thaw cycles | Stable x3 |
Causes for Rejection
Citrate plasma specimen; improper labeling
Test Details
Use
Evaluate thyroid function and assess abnormal binding protein disorders
Limitations
Circulating antibodies to thyroid hormones have also been reported to interfere with free hormone immunoassays.
Methodology
Electrochemiluminescence immunoassay (ECLIA)
Reference Interval
See table.1
Age | Range (pg/mL) |
|---|---|
0 to 3 d | 2.0−7.9 |
4 to 30 d | 2.0−5.2 |
31 d to 12 m | 1.6−6.4 |
13 m to 5 y | 2.0−6.0 |
6 to 10 y | 2.7−5.2 |
11 to 19 y | 2.3−5.0 |
>19 y | 2.0−4.4 |
Additional Information
Triiodothyronine (T3) normally represents only approximately 5% of the thyroid hormone and like thyroxine is almost entirely bound to the carrier proteins, with only 0.25% of the total being in the free state. Measurement of free triiodothyronine is of value in confirming the diagnosis of hyperthyroidism, when an elevated free or total thyroxine level is found. Abnormal total and free triiodothyronine concentrations may appear in T3 toxicosis, in the presence of normal thyroxine levels. Free T3 levels are unaffected by carrier protein variation.
Footnotes
References
LOINC® Map
| Order Code | Order Code Name | Order Loinc | Result Code | Result Code Name | UofM | Result LOINC |
|---|---|---|---|---|---|---|
| 010389 | Triiodothyronine (T3), Free | 3051-0 | 010389 | Triiodothyronine (T3), Free | pg/mL | 3051-0 |
| Reflex Table for Triiodothyronine (T3), Free | ||||||
|---|---|---|---|---|---|---|
| Order Code | Order Name | Result Code | Result Name | UofM | Result LOINC | |
| Reflex 1 | 000000 | |||||
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