What Is the TSH Test?
Whenever your doctor orders blood testing, your lab slip may seem like a confusing list of acronyms that you can't begin to understand. Based on your complaints and the signs that you show during a physical examination, your doctor has a hunch as to what might be wrong, but this can only be confirmed through diagnostic testing. In the case of the TSH test, the answer is fairly simple: this test assesses the function of your thyroid gland.
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Understanding Your Thyroid
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To understand the need for TSH testing, it's helpful to work backward and first take a look at the thyroid gland. This is a small, butterfly-shaped gland located in the front of your neck that consists of two lobes that wrap around your trachea, adjoined with a band of tissue called an isthmus. The thyroid gland has an important job; it takes iodine from the food that you eat and converts it into thyroid hormone, which in turn regulates all aspects of your body's metabolism. The thyroid hormone itself is actually comprised of two different hormones: thyroxine or T4, which either itself to certain proteins to help tissues that need thyroid or enters the tissues directly; and triiodothyronine or T3, which is simply T4 that has been converted by the liver or the brain so that it more efficiently serve these organs.
The Pituitary Gland & TSH
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When it comes to the thyroid gland, the pituitary gland, which is located in your brain, takes on the role of overseer. Whenever the pituitary notes that there isn't enough thyroid hormone in the blood, it produces TSH, or thyroid-stimulating hormone, which is dispatched to the thyroid gland. This signals the thyroid gland to produce more thyroid hormone. After there's enough thyroid hormone present, the pituitary gland stops sending TSH to the thyroid gland. So when diagnosing thyroid disorders, it makes sense to take a look at the amount of TSH present in your blood to see how hard your pituitary gland is working.
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TSH Levels
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Whenever TSH levels are too high and T4 is low, this indicates that either the TSH that the pituitary gland is sending to the thyroid gland is having no effect on thyroid hormone production. Alternately, when TSH levels are low and T4 levels are high, this indicates that the thyroid gland is over-producing. These levels, when looked at together, can indicate that the medical conditions of hypothyroidism and hyperthyroidism are present, respectively. However, TSH and T4 levels won't give your doctor the underlying cause of hypothyroidism or hyperthyroidism, so more comprehensive testing is required.
Other Tests
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A thyroid antibody test--which is another blood test--is used to see if your thyroid disorder is caused by an autoimmune disorder, such as Hasthimoto's thyroiditis or Graves' disease. Also, a radioactive thyroid uptake can determine how much iodine your thyroid is taking in. Sometimes thyroid nodules can cause the thryoid gland to produce too much thyroid hormone--this condition may require more invasive testing procedures, such as a fine needle biopsy, to make sure that the nodules are benign and not cancerous. However, according to the Mayo Clinic, the TSH test is the test that's most sensitive to thyroid disorders; often they can be diagnosed even before you begin to notice symptoms.
Managing Thyroid Disorders
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If you're diagnosed and treated for a thyroid disorder, ongoing TSH testing plays a critical role in managing your condition. TSH testing, in conjunction with T4 testing, can let your doctor know if the hormone replacement that you take to treat hypothyroidism is sufficient, or if the anti-thyroid drugs or other therapies used to treat hyperthyroidism are having the desired effect. To find out more about TSH testing and its role in assessing thyroid functioning, see the Resource link below.
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