Changes in your metabolism—such as shifts in weight, body temperature, or energy levels—may be signs of abnormal thyroid-stimulating hormone (TSH) levels. This thyroid function test measures TSH in your blood to help detect potential thyroid imbalances. Elevated TSH levels may suggest hypothyroidism (underactive thyroid), while low levels may point to hyperthyroidism (overactive thyroid). If your TSH levels are outside the normal range, a reflex T4 test will automatically be performed at no extra cost to further evaluate thyroid function.