Thyroid-Stimulating Hormone

Other names: TSH; Thyrotropin

Thyroid stimulating hormone (TSH) is a hormone, which is formed by the pituitary gland. TSH is part of the feedback loop, which helps to control thyroid hormones, including thyroxine (T4) and triiodothyronine (T3). Thyroid hormones play an important role in regulating the amount of energy used by the body; when levels decrease in the blood, the hypothalamus stimulates the production of TRH (thyrotropin releasing hormone), which in turn stimulates the production of TSH. TSH provokes the release of T3 and T4 by the thyroid gland.

When is the test used?

The TSH test is used to evaluate the function of the thyroid gland; it may be ordered along with tests to measure T3 and T4 levels. The test may be used to monitor patients who are receiving treatment for a thyroid disorder and to screen newborn babies.

The test is usually ordered when a patient has symptoms of either hyperthyroidism (overactive thyroid gland) or hypothyroidism (underactive thyroid gland). Signs of hyperthyroidism include rapid heart rate, nervousness and anxiety, weight loss, insomnia and intolerance to hot temperatures, while symptoms of hypothyroidism include weakness, weight gain, fatigue, intolerance to cold temperatures and slow heart rate.

The test may also be ordered as a routine screening test for newborn babies.

How is the test done?

The test is done by collecting and analysing a sample of blood from the patient’s arm; a needle is inserted into a vein in the arm (usually on the inside of the elbow) and the blood is drawn out using a syringe. When the doctor has a sufficient sample, the blood is bottled, labelled with the patient’s name and sent to the laboratory for analysis.

What do the test results mean?

If the results of the TSH test are high, this usually indicates that the patient has hypothyroidism (underactive thyroid gland); in rare cases, when levels are very high, this may indicate that the patient has a problem with their pituitary gland.

If the results are low, this usually indicates that the patient has hyperthyroidism (overactive thyroid gland); it may also mean that there is damage to the pituitary gland, which is preventing the production of TSH.

The test results show whether there is a problem with thyroid function; however, it cannot determine the cause of the problem and further tests will be required.

If levels are abnormal once the patient has started treatment, this may indicate that the patient is being given a dose which is either too high or too low.

Specific Blood Tests

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