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Thyroid Diseases

Relying on the TSH to adjust thyroid dosing

02/24/2011

Question:

I have read that there is controversy regarding TSH levels and thyroid hormone dosing. If TSH levels are below range but free T4 is within range and there are no hyperthyroid symptoms, then would it be necessary to adjust one`s current dosage?

I had a total thyroidectomy (no cancer) about 11 months ago and am still working on getting the right dose of Synthroid. My latest TSH level is .10 and my free T4 is 1.2 and I feel fine.

Answer:

TSH is made by the pituitary gland at the base of the brain. One of the jobs of the pituitary gland is to constantly test the blood to see if there is enough thyroid hormone in it. If not, it sends out more TSH. If there is too much thyroid hormone in the blood, the pituitary sends out less TSH. Thus, measuring the TSH level in your blood is like asking your own pituitary gland if it thinks there is the right amount of thyroid hormone in your blood. Your TSH of 0.1 indicates that there is too much thyroid hormone in your blood. Over the years, this can weaken your bones and cause osteoporosis. Depending on your age, it could also increase your risk of developing abnormal heart rhythms - nothing that would kill you, but something that would land you in the hospital for a few days, commit you to taking blood thinners for some period of time, and might even cause a stroke. If I were you, I would want my TSH to be normal.

There is a little controversy about the exact normal limits we should be using for TSH levels, but the controversy is at the other end of the normal range. There is some question as to whether or not the upper limit of normal should be 3.0 or 5.5. I don't think that controversy applies to your case.

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Response by:

Thomas A Murphy, MD, FACP, FACE Thomas A Murphy, MD, FACP, FACE
Associate Professor of Medicine
School of Medicine
Case Western Reserve University