Purpose of free T3 thyroid hormone test

Free T3 thyroid hormone test

Thyroid gland produces 2 type of thyroid hormones as T3 –triiodothyronine and T4-thyroxine. Thyroid gland is a small gland in front of your neck below the Adam’s apple. Thyroid hormones are so important for your body metabolism. Thyroid hormones regulates so many body functions like; body temperature, heart rate, energy production, blood pressure, etc.

Thyroid hormones have 2 forms as total T3 and total T4 and free T3 and free T4. Free T3 (fT3) is the active type of the thyroid hormones in your body. T4 is converted to T3 in liver and thyroid gland.

Total T3 value may be affected by several factors but free T3 thyroid hormone level is not affected by these factors and for this reason free T3 test is preferred. Your doctor may request free T3 blood test to evaluate some conditions as listed;

Purpose of free T3 blood test

free t3 hormone analyzers

Your doctor may request free T3 test in these type of conditions;

  • Evaluating thyroid gland functions
  • If your TSH level is low but T4 level is normal
  • If patient’s free T4 level is normal but he/she has toxic goiter symptoms
  • Monitoring hyperthyroid patients
  • Monitoring patients who use thyroid medications
  • Evaluating severity of the toxic goiter
  • Your doctor may request free T3 blood test to evaluate the thyroid disorder symptoms.

Thyroid disease symptoms and free T3 thyroid hormone blood test

thyroid symptoms


  • Weakness
  • Fatigue
  • Weight loss
  • Weight gain
  • Rapid heart rate
  • Depression
  • Constipation
  • Feeling cold
  • Prolonged menstrual bleeding
  • Hair loss
  • Joint pain
  • Dry skin
  • Slow heart rate
  • Poor concentration


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