Thyroid Function Test

What are thyroid function tests?

Thyroid function tests are a group of blood tests used to evaluate the thyroid gland functioning.

Other names for this test are Thyroid profile, Thyroid panel, T3, T4, TSH test, and TFT.

How does the thyroid gland work?

The thyroid, a small gland situated in the lower front part of the neck, plays a crucial role in regulating various bodily processes, including metabolism, energy production, and mood. The thyroid gland produces two significant hormones, triiodothyronine (T3) and thyroxine (T4). Insufficient production of these hormones can lead to weight gain, fatigue, and depression, a condition known as hypothyroidism. On the other hand, excessive hormone production by the thyroid gland can cause weight loss, heightened anxiety, tremors, and a feeling of being overly stimulated or “high,” which is referred to as hyperthyroidism.

Who conducts the thyroid function test?

When the doctor suspects imbalances in thyroid hormone levels, they may order comprehensive screening tests such as the T3, T4, or thyroid- stimulating hormone (TSH) test to assess the functioning of the thyroid gland. Generally, fasting is not required before doing this test. An individual can eat and drink normally unless the doctor suggests otherwise.

A laboratory technician will locate a vein in the arm, clean the site, and insert a small needle to draw blood into a vial. The process typically takes a few minutes. The blood sample will be sent to a lab for analysis.

Who should get a thyroid function (TFT) test?

A thyroid function test is recommended in various situations:
  • If there are signs or symptoms suggestive of thyroid dysfunction
    • Fatigue
    • Weight changes
    • Changes in heart rate
    • Muscle weakness
    • Changes in mood or mental functioning
    • Changes in menstrual patterns
    • Dry skin and hair
    • Sensitivity to cold or heat
  • If an individual is taking medicines that can affect thyroid function, such as amiodarone and lithium
  • If the lady is pregnant
  • If an individual is on thyroid medication such as thyroxine, a thyroid test is recommended to monitor the response to it.

Thyroid Blood Test

Thyroid-stimulating hormone (TSH) test: The TSH test measures the level of thyroid-stimulating hormone in the blood. The pituitary gland produces TSH and stimulates the thyroid gland to produce thyroid hormones. Abnormal TSH levels can indicate hypothyroidism (elevated TSH) or hyperthyroidism (decreased TSH).
Total or Free Triiodothyronine (T3) Test: The T3 test measures the triiodothyronine level in the blood. T3 is another thyroid hormone that plays a role in regulating metabolism. Total or free T3 tests can provide additional information about thyroid function and are sometimes used in conjunction with other tests.
Free Thyroxine (FT4) Test: The FT4 test measures the level of free thyroxine in the blood. Thyroxine (T4) is the primary hormone produced by the thyroid gland. It helps regulate metabolism and energy levels in the body. The FT4 test provides information about the actual level of active thyroid hormone available.
Thyroid antibody tests: Antibody tests help diagnose autoimmune thyroid conditions such as Hashimoto’s thyroiditis or Graves’ disease. Common antibody tests include thyroid peroxidase antibody (TPOAb) and thyroglobulin antibody (TgAb) tests. These tests detect the presence of specific antibodies that attack the thyroid gland. Thyroid antibodies are made when the immune system mistakenly attacks the thyroid gland.

What are normal thyroid levels?

  • Thyroid-stimulating hormone (TSH): 0.4 to 4.0 mIU/L (milli-international units per liter).
  • Free thyroxine (FT4): 0.8 to 1.8 ng/dL (nanograms per deciliter).
  • Triiodothyronine (T3): 80 to 200 ng/dL (nanograms per deciliter).
It is important to note that these reference ranges are approximate and can vary. Additionally, different laboratories may have slightly different ranges, so it is essential to refer to the specific reference range provided by the laboratory where the test was performed. While the thyroid panel is a valuable diagnostic tool, it is important to understand that it cannot independently provide a definitive diagnosis for a thyroid condition. Abnormal results from the thyroid panel require further analysis and interpretation by a doctor. They are the best resource for explaining the specific findings and their significance. They will consider factors such as symptoms, medical history, and additional tests to provide a comprehensive assessment and guide the patient toward appropriate diagnosis and treatment.


  1. American Thyroid Association. Thyroid Function Tests. Available from: https://www.thyroid.org/thyroid-function-tests/
  2. Healthline. Thyroid Function Tests. [Internet]. Available from: https://www.healthline.com/health/thyroid-function-tests#results.
  3. Cleveland Clinic. Thyroid Blood Tests. [Internet]. Available from: https://my.clevelandclinic.org/health/diagnostics/17556-thyroid-blood-tests
  4. Thyroid Panel Test. Available from: https://www.testing.com/tests/thyroid-panel/
  5. Pearce EN, Farwell AP, Braverman LE. Thyroiditis. N Engl J Med. 2003;348(26):2646-2655

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