How to interpret Thyroid function test in your labs?

What is Thyroid function test?


Thyroid gland is a butterfly shaped gland sitting in the neck which regulates thyroid hormone and plays an important role in body metabolism. Thyroid gland function is regulated by feedback loop involving pituitary gland and hypothalamus in brain depending upon circulating thyroid hormone levels. Thyroid hormone is vital for body temperature regulation, metabolism, skin health, digestion, mood, weight management and muscle strength.


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Normal Thyroid lab range for adults: (May vary among various labs)


TSH: 0.4 – 4.5 mIU/L (low TSH means high thyroid and high TSH means low thyroid levels)


Free T4: 0.8 – 1.8 ng/dL


T3 total: 76 – 181 ng/dL


Additional Thyroid labs may be necessary based on TSH, Free T4 and T3 levels.


What are the common causes of low Thyroid levels?


  • Hashimoto’s disease where your immune system attacks the Thyroid gland and decreases the production of Thyroid hormone

  • Thyroiditis – inflammation of thyroid gland

  • Damage to Thyroid gland from radiation

  • Damage to Thyroid gland from certain medicines

  • Surgical removal of Thyroid gland such as in those with Thyroid cancer

  • Pituitary gland (in brain) disorder

  • Low iodine intake


What are the common causes of high Thyroid levels?


  • Grave’s disease where your immune system stimulates the Thyroid gland and increases the production of Thyroid hormone

  • Inflammation of Thyroid gland

  • Hyperactive Thyroid nodule

  • Too much of iodine

  • Too much of thyroid replacement medicine


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