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  • About this test

    Thyroid-stimulating hormone (TSH) is produced by the pituitary gland and stimulates the thyroid gland to release the hormones thyroxine (T4) and triiodothyronine (T3) into the blood. This test measures the amount of TSH in the blood.

    The function of T4 and T3 is to control the rate at which the body uses energy.

    • When thyroid hormone levels decrease in the blood the pituitary gland produces more TSH to stimulate the thyroid to produce and release more T4 and T3.
    • When thyroid hormone levels increase in the blood the pituitary gland produces less TSH and subsequently the thyroid produces less T4 and T3.

    Hyperthyroidism (overactive thyroid) results in release of inappropriately large amounts of T4 and T3 with symptoms of rapid heart rate, weight loss, nervousness, hand tremors, irritated eyes and sleeping difficulty.

    Hypothyroidism (underactive thyroid) results in a decreased production of thyroid hormones by the thyroid with symptoms of weight gain, dry skin, constipation, cold intolerance, and fatigue.

    A TSH test is frequently ordered along with a free T4 test. TSH testing may be used with free T4 to:

    • Help diagnose a thyroid disorder in a person with signs and symptoms
    • Monitor thyroid replacement therapy (hypothyroidism)
    • Monitor anti-thyroid treatment (hyperthyroidism)

    Who is this test for?

    TSH is often ordered in the presence of symptoms of an overactive or underactive thyroid. It could also be used as part of a general health screen.

    Signs and symptoms of overactive thryroid (hyperthyroidism) may include:

    • Rapid heart rate
    • Feelings of anxiety
    • Unexpected weight loss
    • Sleeping difficulty
    • Hand tremors
    • Weakness
    • Diarrhoea
    • Light sensitivity and visual disturbances
    • Eye puffiness, dryness and
    • Menstrual irregularities

    Signs and symptoms of underactive thyroid (hypothyroidism) may include:

    • Consistent weight gain
    • Dry skin
    • Constipation
    • Cold intolerance
    • Hair loss
    • Fatigue
    • Menstrual irregularities and fertility problems

    TSH may be ordered more frequently as part of monitoring for patients who are being treated for specific thyroid conditions.