— M.R. Answer:

Dear Dr. Roach:

A few months ago, I had routine follow-up thyroid tests, and my results were normal except for a slightly high free T4 level. My doctor decreased my medication dose to 137 mcg from 150 mcg; now my TSH is high (8.77), but my free T4 and T3 levels are normal.

Fatigue is my biggest symptom, and I am often chilly. I do have some constipation, for which I have been taking a stool softener for a number of years.

In an ideal world, people with symptoms of low thyroid would have consistent laboratory findings: low thyroid hormone levels, both T4 (thyroxine, the medicine you are taking) and T3 (the active form of thyroid hormone); and a high TSH level (the hormone your body uses to regulate the thyroid). A higher TSH means the body is trying to make the thyroid put out more thyroid hormone.

However, it doesn’t always work the way it should. People can have symptoms with normal labs. The TSH and the T3/T4 can point in different directions. When that happens, I base treatment mostly on symptoms, not numbers. Of course, the hormone levels are important too: If the T3 and T4 get too high, it increases the rate of atrial fibrillation and can adversely affect the bones.

In your case, your doctor has a choice: On one hand, there is a normal T4, a high TSH and symptoms of low thyroid; on the other, there is a slightly high T4, but normal TSH and no symptoms. While I am oversimplifying a bit, the better choice (to use the higher 150-mcg dose and treat the symptoms) seems easy to me.

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