Walk-In Lab’s thyroid-stimulating hormone (TSH) blood test helps diagnose thyroid gland disorders such as hyperthyroidism. It is often ordered alongside a T4 blood test and a T3 blood test.The TSH blood test is also known as a Third-Generation TSH or Thyrotropin. Fasting is not required before taking the test and results are available within one to two days.TSH is a thyroid function test used to assist in the diagnosis of thyroid disorders, monitor thyroid replacement therapy in patients with hypothyroidism, diagnose and/or monitor female infertility problems, and occasionally the test is used to help evaluate pituitary gland function. While the test is most often used to help diagnose thyroid disorders in adults, expert opinions vary on the benefits of screening, and at what age to begin testing.The test investigates for low thyroxine (T4); the differential diagnosis of primary hypothyroidism from normal, and the differential diagnosis of primary hypothyroidism from pituitary/hypothalamic hypothyroidism. High TSH levels are found primarily in hypothyroidism, while low TSH occurs in hyperthyroidism. When evaluating the effectiveness of therapy for hypothyroid patients receiving thyroid hormone preparation, low TSH values are typically found in states of excessive thyroid replacement. Normal results on a sensitive TSH blood test is therefore considered acceptable evidence of adequate thyroid replacement.Additionally, a TSH assay can be considered when testing for thyroid disease. Results within the accepted reference interval provide strong evidence for euthyroidism, or a normally functioning thyroid.