Simple Clinical Meaning
An anterior pituitary hormone that stimulates the thyroid gland to produce and secrete thyroxine (T4) and triiodothyronine (T3). The most sensitive screening test for thyroid dysfunction.
Detailed Clinical Explanation
Operates on an inverse negative feedback loop with thyroid hormones:
- Reference Range: Typically 0.4 to 4.5 mIU/L.
- Elevated TSH (>4.5 mIU/L): Indicates primary hypothyroidism (the pituitary produces excess TSH to stimulate an underactive thyroid).
- Suppressed / Low TSH (<0.4 mIU/L): Indicates hyperthyroidism or thyrotoxicosis (excess circulating T3/T4 suppresses pituitary secretion).
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