If your doctor suspects a thyroid disorder, a blood test can help provide an answer. This test measures the level of thyroid stimulating hormone (TSH), a kind of master hormone that regulates the work of the thyroid gland. Along with TSH measurements , thyroid hormone levels are also analyzed. If TSH is high, it typically means that your thyroid function is too low (hypothyroid). If TSH is low, then it generally means the thyroid is overactive (hyperthyroid.) Your doctor may also check levels of other thyroid hormones in your blood. In some cases, imaging studies are used and biopsies are taken to evaluate a thyroid abnormality.