What Does TSH (Thyroid Stimulating Hormone) Mean?
TSH tells your thyroid to produce thyroid hormones. High TSH suggests the thyroid isn't making enough hormone (hypothyroidism). Low TSH may indicate an overactive thyroid.
What TSH (Thyroid Stimulating Hormone) Measures
TSH is made by the pituitary gland and tells your thyroid gland how much thyroid hormone (T4 and T3) to produce. When thyroid hormone is low, the pituitary makes more TSH to stimulate the thyroid — so high TSH usually means an underactive thyroid (hypothyroidism).
Normal Ranges
Normal0.4–4.0 mIU/L
Subclinical hypothyroid4.0–10.0 mIU/L
Overt hypothyroid> 10.0 mIU/L
Hyperthyroid< 0.4 mIU/L
Reference ranges may vary slightly by lab. Always use the range provided on your specific test report.
What Affects Your TSH (Thyroid Stimulating Hormone) Level
- Hashimoto's autoimmune thyroiditis (most common cause of hypothyroid)
- Iodine deficiency or excess
- Selenium deficiency
- Certain medications (lithium, amiodarone)
- Pregnancy (TSH fluctuates naturally)
- Stress and sleep deprivation