Thyroid-Stimulating Hormone (TSH) Test

TSH, Hyperthyroidism, & Hypothyroidism

Thyroid gland, Image from WikimediaThyroid-stimulating hormone (TSH) test is used to diagnose hyperthyroidism and hypothyroidism. It is ordered when a patient shows signs and symptoms of hypo- and hyperthyroidism. Hypothyroidism is the deficiency in the production of thyroid hormones; symptoms include weight gain, constipation, dry skin, fatigue, and cold intolerance. Hyperthyroidism is the overproduction of thyroid hormones at dangerously high levels; symptoms include sleeping difficulty, irritated eyes, nervousness, tremors, weight loss, and rapid heart rate. Thyroxine (T4) and triiodothyronine (T3) are the two types of hormones produced by the thyroid gland – small butterfly-shaped gland that lies in the neck flat against the windpipe. T4 and T3 are responsible in controlling metabolism and growth
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Functions of TSH

TSH is produced by the pituitary gland, a small oval gland at the base of the brain and just behind the sinus cavities. TSH maintains the stable level of thyroid hormones in the blood by stimulating the production and release of T4 and T3 by the thyroid gland. When the amount of thyroid hormones in the blood declines, the hypothalamus releases thyrotrophin-releasing hormone which stimulates the release of TSH by the pituitary gland. Any abnormality to the thyroid gland, pituitary gland, or the hypothalamus can result to hypo- or hyperthyroidism.

TSH Test

TSH test measures the amount of TSH in the blood. It is often ordered together with T3 and T4 tests to diagnose hyper- and hypothyroidism. The test is also used to monitor the improvement of a patient receiving treatment for thyroid disorder.

A healthcare provider will draw blood from your arm for laboratory testing. The test results will be interpreted by your doctor. You should not take certain medications before the test because they can interfere with the results. These medications include propylthiouracil, methimazole, lithium, dopamine, heparin, levodopa, corticosteroids, and others. You should tell your doctor all medications you are taking before the test.

Interpretation of TSH Test Results

An underactive thyroid gland results to the increase in blood TSH level as the pituitary gland is continuously releasing TSH to get the thyroid gland respond and produce more hormones. According to AACE, TSH level below 0.3 mlU/L is considered low as the normal range for blood TSH is 0.3-3.0 mIU/L. A high TSH level but with normal T4 and T3 levels is considered mild or subclinical hypothyroidism. Moreover, a high TSH level but with low T4 and T3 levels is considered hypothyroidism.

An overactive thyroid gland results to the decrease in blood TSH level as the pituitary gland slows down or even stops releasing TSH when it senses that there is too much thyroid hormones in the blood. Hyperthyroidism occurs when the thyroid gland keeps on producing hormones even without being stimulated by the TSH. A low TSH level but with normal T4 and T3 levels is considered mild or subclinical hyperthyroidism. A low TSH level but with high or normal T4 and T3 levels is considered hyperthyroidism.

Disease or injury to the thyroid gland can both results to hyper- or hypothyroidism. But disease or injury to both the hypothalamus and pituitary gland can also result to hyper- or hypothyroidism. For example, tumor to the pituitary gland can cause elevation or deficiency in thyroid hormones. A low TSH level with low or normal T4 and T3 levels is considered non-thyroidal disease or rare pituitary (secondary) hyperthyroidism.[ad#afterpost]
References and Further Reading