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About the test
What is this test done for?
Free T3, Free T4 & TSH; also known as FT3, FT4 & TSH; are a set of blood tests that are carried out to evaluate levels of active T3, active T4 and TSH of the blood.
Why is it Done?

This is a specialized blood test that evaluates the amount of thyroid hormones in the blood. It screens for Free T3 (tri-iodothyronine), Free T4 (tetra-iodothyronine) and TSH (thyroid stimulating hormone). The test is carried out for

  • Ruling out hypothyroidism
  • Ruling out hyperthyroidism

Free T4 and TSH levels help in confirming the diagnosis of hypothyroidism as well as hyperthyroidism but Free T3 levels only help in testing for hyperthyroidism or assessing its severity.

When should it be performed?

This test is performed when a patient has

  • Symptoms of hypothyroidism
    • Obesity
    • Easy fatigability
    • Constipation
    • Increased sensitivity to cold
    • Weight gain
    • Puffy face
    • Dry skin
    • Muscle weakness
    • Pain, stiffness & swelling of joints
    • Irregular menstrual periods
    • Thinning of hair
    • High levels of cholesterol in blood
    • Slow heart rate
    • Impaired memory or depression
  • Symptoms of hyperthyroidism
    • Sudden weight loss
    • Increased appetite
    • Rapid heart beat
    • Tremors (fine trembling of hands and fingers)
    • Increased sweating (hyperhydrosis)
    • Increased bowel frequency
    • Increased sensitivity to heat
    • Changes in menstrual pattern
    • Nervousness, anxiety and irritability
    • Fatigue and muscle weakness
    • Thin and brittle hair
  • Existing thyroid disorder, the test is done regularly to monitor
  • History of post partum thyroiditis
  • Undergoing radiation therapy for cancer of head, face or neck
  • Rheumatoid arthritis patients undergoing treatment with amiodarone or lithium, then 6-12 months during treatment and 12 months after the treatment
How is it done
A blood sample will be collected from a vein in your arm. No special preparations like fasting required.

The test result is normal; if levels of Free T3 are 3.5-7.8 pmol/L, levels of Free T4 9.0-25.0 pmol/L and TSH levels are 0.5-5.0 mU/L. It means

  • Absence of any thyroid disease (Euthroidism)
  • Adequate thyroxine dose for treating hypothyroidism
  • Adequate therapy of hyperthyroidism

If TSH levels are > 10 mU/L (high) and Free T4 levels are <5.0 pmol/L (low); it indicates

  • Hypothyroidism
  • Poorly controlled hypothyroidism
  • Over controlled hyperthyroidism

If TSH levels are < 0.5 mU/L (low) and Free T4 levels are > 25.0 pmol/L (high); it indicates

  • Hyperthyroidism
  • Poorly controlled hyperthyroidism
  • Over controlled hypothyroidism

If TSH levels are > 5 mU/L but < 10 mU/L and Free T4 levels are 9.0-25.0 pmol/L; it means

  • Subclinical hypothyroidism

If TSH levels are < 0.5 mU/L (low) and Free T4 levels are < 9 pmol/L (low); it means

  • Hypopituitarism
  • Secondary hypothyroidism
  • Response to a significant non-thyroid illness

If Free T3 levels are > 8 pmol/L (high), it means

  • Hyperthyroidism

If Free T3 levels are very high, it means severe form of hyperthyroidism.

Other Tests
  • TSH
    • It is a routine blood test carried out to evaluate TSH (thyroid stimulating hormone) levels of blood
    • Low TSH levels suggest hyperthyroidism or over controlled hypothyroidism
    • High TSH levels suggest hypothyroidism or poorly controlled hypothyroidism
  • T3 T4 and TSH
    • It is a routine blood test that evaluates total T3, total T4 and TSH levels of blood
    • Low T4 level and high TSH levels suggest hypothyroidism whereas high T4 and low TSH levels suggest hyperthyroidism or excessive dose of thyroxine to treat hypothyroidism
  • Anti TPO antibodies
    • It is a specialized blood test carried to evaluate anti TPO antibodies in the blood
    • Presence of Anti TPO antibodies suggest the cause of hypothyroidism as autoimmune thyroiditis
  • TRAb (TSH receptor antibodies)
    • This is a specific test for ruling out Grave’s disease
  • Thyroglobulin antibodies
    • This test is done for checking antibodies against thyroglobulin
    • It indicates the cause of thyroid disease as Hashimoto’s thyroiditis or idiopathic myxedema
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