T3, Free
Test Mnemonic
FREET3
CPT Codes
- 84481 - QTY (1)
LOINC ®
3051-0
Aliases
- Triiodothyronine, Free
Performing Laboratory
Cleveland Clinic Laboratories
Specimen Requirements
| Volume | Type | Container | Collect Temperature | Transport Temperature | Special Instructions |
|---|---|---|---|---|---|
| 1 mL | Plasma | Lithium heparin PST (Lt. Green) | Centrifuge and refrigerate. | Submit in original tube or aliquot into CCL aliquot tube |
Alternate Specimen Requirements
| Volume | Type | Container | Collect Temperature | Transport Temperature | Special Instructions |
|---|---|---|---|---|---|
| 1 mL | Serum | SST (Gold) | Centrifuge and refrigerate. |
Minimum Specimen Requirements
| Volume | Type | Container | Collect Temperature | Transport Temperature | Special Instructions |
|---|---|---|---|---|---|
| 0.5 mL |
Stability
| Environmental Condition | Description |
|---|---|
| Ambient | 5 days |
| Refrigerated | 7 days |
| Frozen | 30 days |
Days Performed
Sun - Sat
Turnaround Time
8 hours
Methodology
| Name | Description |
|---|---|
| Electro Chemiluminescence Immunoassay (ECLIA) |
Reference Range
| T3, Free | |||||
|---|---|---|---|---|---|
| Sex | Age From | Age To | Type | Range | Range Unit |
| Days | 3 Days | Normal | 1.4 - 5.4 | pg/mL | 4 Days | 30 Days | Normal | 2.0 - 5.2 | pg/mL | 31 Days | 364 Days | Normal | 1.5 - 6.4 | pg/mL | 1 Years | 6 Years | Normal | 2.0 - 6.0 | pg/mL | 7 Years | 11 Years | Normal | 2.7 - 5.2 | pg/mL | 12 Years | 17 Years | Normal | 2.3 - 5.0 | pg/mL | 18 Years | 99 Years | Normal | 2.3 - 4.1 | pg/mL |
Special Info
Clinical Info
Triiodothyronine (T3) is one of the major thyroid hormones, along with thyroxine (T4). T3 has greater biological activity than T4 and is considered the metabolically active form of thyroid hormone. The activity of T3 is directly regulated by thyroxine binding globulin (TBG), but T3 binds less strongly to TBG than T4. Free T3 represents just a fraction of total circulating T3 (about 0.3%), but free T3 is not affected by protein levels. This assay is usually ordered to diagnose a type of hyperthyroidism known as thyrotoxicosis. In thyrotoxicosis, T3 values are high while T4 (total or free) is normal and TSH is low. Decreased T3 levels occur in drug therapy with androgens, prednisone, dexamethasone, and glucocorticoids. Decreased T3 levels also occur in iodine deficiency, non-thyroidal disease also known as low T3 syndrome, anorexia nervosa, and following surgery to remove the thyroid gland.