A Free T4 Thyroxine test helps diagnose disorders of the thyroid. The thyroid is a small, butterfly-shaped gland located near the throat. Your thyroid makes hormones that regulate the way your body uses energy. It also plays an important role in regulating your weight, body temperature, muscle strength, and even your mood. Thyroxine, also known as T4, is a type of thyroid hormone. This test measures the level of T4 in your blood. Too much or too little T4 can indicate thyroid disease.

The T4 hormone comes in two forms:

Free T4, which enters the body tissues where it's needed.
Bound T4, which attaches to proteins, preventing it from entering body tissues.

this test measures both free and bound T4 is called a total T4 test. Other tests measure just free T4. A Free T4 test is considered more accurate than a total T4 test for checking thyroid function.

Other names: free thyroxine, free T4, total T4 concentration, thyroxine screen, free T4 concentration


To evaluate thyroid gland function, to diagnose thyroid disease, and to monitor thyroid treatment effectiveness.

In newborns, a free T4 can be used to diagnose congenital hypothyroidism.


Testing should be done if there are symptoms of thyroid disease present, and if you have a goiter (an enlarged thyroid) or a thyroid nodule. Testing should be done to monitor the effectiveness of thyroid disorder treatment.

  • Why do I need this test?

  • Thyroid disease is much more common in women and most often occurs under the age of 40. It also tend to run in families. You may need a thyroxine test if a family member has ever had thyroid disease or if you have symptoms of having too much thyroid hormone in your blood, a condition called hyperthyroidism, or symptoms of having too little thyroid hormone, a condition called hypothyroidism.
  • Symptoms of hyperthyroidism, also known as overactive thyroid, include:
  • Anxiety
  • Weight loss
  • Tremors in the hands
  • Increased heart rate
  • Puffiness
  • Bulging of the eyes
  • Trouble sleeping
  • Symptoms of hypothyroidism, also known as underactive thyroid, include:
  • Weight gain
  • Fatigue
  • Hair loss
  • Low tolerance for cold temperatures
  • Irregular menstrual periods
  • Constipation
Free T4 Thyroxine

Free T4 Thyroxine

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Note: The medical information provided here in this website is for informational purposes only and is not to be used as a substitute for professional medical advice, diagnosis or treatment.