Normal Reference Ranges
Adult
2.3 - 4.2 pg/mL
Pediatric
2.6 - 4.8 pg/mL
Clinical Significance
The active form of thyroid hormone. Useful when hyperthyroidism is suspected but Free T4 is normal (T3 toxicosis).
Causes of High
- Hyperthyroidism (Graves' disease, Toxic nodule)
- T3 Thyrotoxicosis
Causes of Low
- Hypothyroidism
- Non-thyroidal illness (Euthyroid sick syndrome)