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THYROID FUNCTION TEST

  • Why get tested?

To help check if the thyroid gland is working normally, to help diagnose thyroid disorders and to
monitor the response to treatment.

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  • When to get tested?

As part of a health check-up when symptoms suggest the thyroid gland has either reduced or
increased activity. Alternatively during a course of treatment for a disorder of the thyroid gland.

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  • Is test preparation needed?

None needed; however, if you are on medication then inform about it at the time of sample
collection.

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  • What is being tested?

TFTs measure the amount of the thyroid hormones, Thyroxine (T4) or Tri-iodothyronine (T3)
and/or the pituitary hormone, Thyroid Stimulating Hormone (TSH) in your blood. These
hormones travel through the bloodstream and control or regulate how fast your body uses
energy. Thyroid hormones are present in the blood in either protein bound forms (the majority)
or the free and active form of the hormone – Free T4 (FT4) or Free T3 (FT3).
Thyroid Function Tests usually include some combination of:

  1. TSH (thyroid stimulating hormone or thyrotropin)– to test for hypothyroidism and hyperthyroidism and to      monitor thyroid replacement therapy

  2. T4 – to test for hypothyroidism and hyperthyroidism

  3. T3 – to test for hyperthyroidism

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  • When is it requested?

TFTs may be requested as part of a health check-up when symptoms suggest hypo- or
hyperthyroidism due to a condition affecting the thyroid. They may also be requested following
commencement of treatment for any detected thyroid condition.

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Signs and symptoms of hypothyroidism (decreased function of the thyroid) may include weight gain, dry skin, constipation, cold intolerance, puffy skin, hair loss, fatigue, and menstrual irregularity in women. Signs and symptoms of hyperthyroidism (increased function of the thyroid) may include increased heart rate, anxiety, weight loss, difficulty sleeping, tremors in the hands, weakness, and sometimes diarrhoea. There may be puffiness around the eyes, dryness, irritation, and, in some cases, bulging of the eyes

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  • What does the test result mean?

The following table summarizes test results and their potential meaning :

TSH

Normal

High

High

Low or Undetectable

TOTAL T4

Normal

Normal

Low

Normal

TOTAL T3

Normal

Normal

Normal & low

Normal

THYROID FUNCTION

Normal thyroid function

Subclinical hypothyroidism

Primary hypothyroidism related to the thyroid gland

Subclinical hyperthyroidism

Low

High

High

Primary hypothyroidism related to the thyroid gland

Low

Low

Low & Normal

Secondary hypothyroidism related to the pituitary gland

Normal or high

High

High

Secondary hypothyroidism related to the pituitary gland

  •  What conditions are associated with hypo and hyperthyroidism?

Common causes of thyroid dysfunction are autoimmune related; Graves’ disease causes hyperthyroidism, and Hashimoto’s thyroiditis causes hypothyroidism. Both hyper- and hypothyroidism can also be caused by thyroiditis (or thyroid inflammation including after childbirth), thyroid cancer, and excessive or deficient production of TSH. Another common cause of an over-active thyroid is a thyroid nodule or multi-nodular goitre.

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  •  What other tests may be requested in addition to TFT ?

Tests that may be performed in addition to TFTs may include :

  • Free T3

  • Free T4

  • Thyroid peroxidase antibodies ( Anti TPO )

  • Thyroglobulin antibodies (thyroglobulin antibodies)

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