This is for informational purposes only. For medical advice or diagnosis, consult a professional. The Thyroid Stimulating Hormone (TSH) test is a blood test that measures the amount of TSH in your blood. TSH is a hormone produced by the pituitary gland that stimulates the thyroid gland to produce thyroid hormones (T3 and T4). This test is primarily used to:   Diagnose thyroid disorders: Including hypothyroidism (underactive thyroid) and hyperthyroidism (overactive thyroid).   Monitor thyroid treatment: For people already diagnosed with a thyroid condition, it helps ensure their medication dosage is correct.