TSH stands for thyroid-stimulating hormone. It is produced by the pituitary gland — a pea-sized gland at the base of your brain — and its job is to tell your thyroid gland how much hormone to make.
How TSH Works in the Body
TSH travels through your bloodstream to your thyroid gland. When TSH binds to receptors on thyroid cells, it triggers the production of two key hormones: T3 (triiodothyronine) and T4 (thyroxine). These hormones regulate your metabolism, energy levels, body temperature, heart rate, and much more.
The system works on a negative feedback loop:
- When T3/T4 levels are low → pituitary releases more TSH.
- When T3/T4 levels are high → pituitary releases less TSH.
TSH vs. T3 and T4
| Hormone | Produced By | Main Role |
|---|---|---|
| TSH | Pituitary gland | Signals the thyroid to work |
| T4 | Thyroid gland | Inactive storage hormone |
| T3 | Thyroid + converted from T4 | Active hormone that regulates metabolism |
Why TSH Testing Matters
Because TSH responds before T3 and T4 levels change dramatically, it is the most sensitive early indicator of thyroid dysfunction. A simple TSH blood test can catch hypothyroidism or hyperthyroidism in its earliest stages.
Learn More
Explore our guides on TSH levels, normal ranges, and TSH reference ranges by age and gender.
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