A Thyroid Function Test (TFT) is a group of blood tests used to evaluate how well your thyroid gland is working. The thyroid gland produces hormones that regulate the body’s metabolism, energy generation, and many other vital functions. Here’s a breakdown of the key components of a TFT and what they indicate:
Key Tests in a Thyroid Function Panel
- TSH (Thyroid Stimulating Hormone)
- Most sensitive test for detecting thyroid dysfunction.
- High TSH: Suggests hypothyroidism (underactive thyroid).
- Low TSH: Suggests hyperthyroidism (overactive thyroid) or pituitary dysfunction.
- Free T4 (Thyroxine)
- Measures the active form of T4 hormone.
- Low Free T4 with high TSH: Confirms primary hypothyroidism.
- High Free T4 with low TSH: Indicates hyperthyroidism.
- Free T3 (Triiodothyronine)
- Often used when hyperthyroidism is suspected.
- Elevated in hyperthyroidism, even if T4 is normal.
- Total T4 and T3
- Includes both bound and free hormone levels.
- Less commonly used due to variability from protein levels.
- Thyroid Antibodies
- TPOAb (Thyroid Peroxidase Antibodies) and TgAb (Thyroglobulin Antibodies): Help diagnose autoimmune thyroid diseases like Hashimoto’s thyroiditis or Graves’ disease.
How It Works
The thyroid-pituitary feedback loop functions like a thermostat:
- Low thyroid hormone → pituitary releases more TSH.
- High thyroid hormone → pituitary reduces TSH production [1].
When Is It Ordered?
- Symptoms of thyroid dysfunction (fatigue, weight changes, palpitations, etc.)
- Routine screening (especially in older adults or pregnant women)
- Monitoring thyroid disease or medication
Would you like help interpreting specific test results or understanding what your numbers mean?