Test Details: Thyroid-stimulating hormone (TSH) signals the thyroid gland to make hormones that control how your body uses and stores energy, called your metabolism. Testing the level of TSH in your blood can reveal if your thyroid gland is functioning normally. The level of TSH is tightly controlled by the levels of other thyroid hormones in your blood. High TSH levels may indicate that your thyroid is underactive and needs to be stimulated more, which is called hypothyroidism. Low levels may mean it’s overactive and needs to be stimulated less, called hyperthyroidism.