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What Does the Thyroid Do?

What does the thyroid gland do? What do thyroid tests mean?

By
Rob Lamberts, MD,
May 26, 2010
Episode #048

Page 3 of 4

How Does the Thyroid Affect Metabolism?

That doesn’t mean that high thyroid levels help you run fast, but it does mean that people with overactive thyroid glands tend to have higher heart rates; their muscles shake, and they lose weight. This is called hyperthyroidism. People with under-active thyroid glands, on the other hand, have slower heart rates, are fatigued, and gain weight. That is called hypothyroidism. Children use much of their energy to grow, so children with hypothyroidism don’t grow well.

I am sure there are people out there thinking, “I sure wish I had hyperthyroidism so I could lose weight.” In fact, some doctors give extra thyroid hormone supplements to help people lose weight. That is a big mistake, as hyperthyroidism is actually more dangerous than hypothyroidism. Besides, what do you think the pituitary gland does when you take extra thyroid hormone? It lowers the TSH, which makes the thyroid gland put out less of its own hormones.

What are Thyroid Tests?

I’ll end this week’s article by explaining the significance of thyroid blood tests, which are extremely confusing to both doctors and patients. There are three main levels of thyroid hormones that are important: The TSH level, which we know the pituitary gland releases, and levels of two hormones released by the thyroid itself, known as T3 and T4. To make things even more confusing, there are two types of T3 and T4 found in the blood. The majority of thyroid hormone is bound to protein and is inactive; the active portion is present in very low concentrations and is called the free T3 and Free T4. Unfortunately, the standard tests for T3 and T4 test for the total T3 and T4, not the more important free hormone concentrations. That can make these numbers quite misleading.

So, here are my Quick and Dirty Tips for interpreting thyroid lab tests (listen up, doctors):

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