TSH
Thyroid-stimulating hormone (TSH) is produced by the anterior pituitary gland and controls thyroid hormone production. TSH operates through a negative feedback loop: when thyroid hormones (T3, T4) are low, TSH rises to stimulate the thyroid; when thyroid hormones are adequate, TSH decreases. TSH is the most sensitive marker of thyroid function.
Why it matters: TSH is the first-line screening test for thyroid dysfunction because it amplifies small changes in thyroid hormone levels — TSH can change 10-fold while T3/T4 change only 2-fold. High TSH indicates hypothyroidism (underactive thyroid); low TSH indicates hyperthyroidism (overactive thyroid). Subclinical thyroid disease (abnormal TSH with normal T3/T4) is very common and often missed.
May increase with:
May decrease with:
What is TSH?
Thyroid-stimulating hormone (TSH) is produced by the anterior pituitary gland and controls thyroid hormone production. TSH operates through a negative feedback loop: when thyroid hormones (T3, T4) are low, TSH rises to stimulate the thyroid; when thyroid hormones are adequate, TSH decreases. TSH is the most sensitive marker of thyroid function.
What might a high or low TSH mean?
TSH is the first-line screening test for thyroid dysfunction because it amplifies small changes in thyroid hormone levels — TSH can change 10-fold while T3/T4 change only 2-fold. High TSH indicates hypothyroidism (underactive thyroid); low TSH indicates hyperthyroidism (overactive thyroid). Subclinical thyroid disease (abnormal TSH with normal T3/T4) is very common and often missed.
What is the typical reference range for TSH?
The general-population reference range shown here is 0.55 – 4.78 mU/L. Reference ranges describe the general population and are not a personal target — discuss your results with your physician.
What can affect TSH?
It may be higher with: Primary hypothyroidism (Hashimoto's thyroiditis), Iodine deficiency, Thyroid surgery or radioactive iodine ablation, Lithium therapy, Amiodarone, Recovery phase of non-thyroidal illness, Pituitary TSH-secreting adenoma (rare), Biotin supplements (can interfere with assay — stop 48h before test). It may be lower with: Graves' disease (most common cause of hyperthyroidism), Toxic nodular goiter, Excess thyroid hormone replacement, Subacute thyroiditis (transient), High-dose corticosteroids, Central hypothyroidism (pituitary/hypothalamic), First trimester pregnancy (hCG cross-stimulates TSH receptor), Non-thyroidal illness (sick euthyroid).