About the TSH Test

If the doctor suspects that you have hypothyroidism,
a TSH test will be done

This simple blood test is the best way for you and your doctor to learn if the level of a specific thyroid hormone, called thyroxine, is too low. For the millions of people with hypothyroidism who may show no symptoms, a TSH test may also be needed to check the level of thyroxine.

About the TSH test

A TSH test measures the amount of Thyroid-Stimulating Hormone, or TSH, in your blood. It is the most valuable test for diagnosing hypothyroidism. To work well and feel good, your body needs a precise amount of thyroid hormone. Your pituitary gland makes and sends TSH through your bloodstream. Your pituitary is a pea-sized gland located at the base of your brain. It is like a thermostat. It sends out TSH as a message to "turn on" the thyroid gland to make more thyroxine or "turn off" the thyroid gland to make less. When your thyroid cannot make enough hormone, your pituitary keeps sending the message by making more TSH. This causes a high level of TSH in your blood. A high TSH level means the level of thyroxine in your body is low.


Think of your TSH level and your thyroxine level as two ends of a seesaw. When your TSH level is too HIGH, your thyroxine level is too LOW. This is a sign that you have hypothyroidism.

 Thyroxine Level

Using the same sample of blood drawn for the TSH test, your doctor may also check your "FT4" level. This blood test measures the amount of thyroxine available for your body to use. The blood test is called free thyroxine, or FT4. A low FT4 level may also mean hypothyroidism.

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