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Underactive Thyroid

How Is This Condition Diagnosed?

Many symptoms of hypothyroidism can occur in other diseases, so an underactive thyroid usually cannot be diagnosed based on symptoms alone.
Healthcare providers take a complete medical history, asking detailed questions, and perform a thorough physical examination. Providers may then use several tests to confirm a diagnosis of hypothyroidism and find its cause. This includes blood tests for thyroid-stimulating hormone (TSH) levels.
The TSH test is usually the first test a healthcare provider performs. It is the most accurate measure of thyroid activity available because TSH can be elevated even with small decreases in thyroid function.
The test is based on the way TSH and thyroid hormones work together. The pituitary gland boosts TSH production when the thyroid is not making enough thyroid hormones; the thyroid normally responds to TSH by making more hormones. Then, when the body has enough thyroid hormones circulating in the blood, TSH output drops.
In people who produce too little thyroid hormones, the pituitary makes TSH continuously, trying to get the thyroid to produce more hormones in response.
(Click Diagnosing Hypothyroidism to learn about other tests that may be ordered.)

Treating an Underactive Thyroid

There are two goals with hypothyroidism treatment: return levels of TSH and T4 to normal levels and improve symptoms caused by low thyroid hormone levels. This is done with thyroid hormone replacement therapy.
Thyroid hormone replacement therapy involves taking medicine such as levothyroxine, Levoxyl®, Synthroid®, Tirosint®, Levothroid®, or Unithroid®. In most cases, these medications can completely control the condition. They contain synthetic thyroxine to return thyroid hormone levels to normal. Synthetic thyroxine is identical to the T4 made by the thyroid.
These are not "one-size-fits-all" medications, and there is no "standard" dosage. People have varying degrees of hypothyroidism and, as a result, their dose is individualized.
(Click Treatment for Underactive Thyroid to learn more about managing this condition, along with general outcomes.)
Last reviewed by: Arthur Schoenstadt, MD
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