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Thyroid Diseases

Subclinical Hypothyroidism

02/16/2006

Question:

What is subclinical hypothyroidism? My TSH, 3rd generation, level is 3.71. Does this call for treatment/medication? I have no other symptoms.

Answer:

The thyroid gland knows how to make thyroid hormone, but it doesn't know how much thyroid hormone to make.  It has to get that information from another gland in the body, the pituitary gland.  The pituitary gland is located at the base of the brain, and one of it's jobs is to constantly test the blood to see if there is enough thyroid hormone in it.  If not, it sends out a hormone called Thyroid Stimulating Hormone (TSH)  that travels to the thyroid gland and stimulates it to make more thyroid hormone.  Thus, measuring the amount of TSH in the blood is like asking the body's own pituitary gland whether it thinks there is enough thyroid hormone around or not. 

Subclinical hypothyroidism is a situation in which the TSH level is abnormal, but the measurement of the actual thyroid hormone level in the blood is within normal limits.  We interpret this to mean that the thyroid hormone level is actually a little low for that person's body, but only a tiny bit low.  It is not clear that having a normal thyroid hormone level and an elevated TSH level hurts you in any way. 

There are two expert reports that have advised us on what to do in this situation - one published in the Journal of the American Medical Association in January of 2004, and another published a few months later in the Journal of Clinical Endocrinology and metabolism.  Both of them suggest repeating the test after 2-12 weeks to be sure the abnormality is not a temporary one.  If the TSH is still high and the free T4 is still normal, opinions differ as to whether or not thyroid hormone should be prescribed. 

The first article says that it is not necessary to treat subclinical hypothyroidism unless the TSH is over 10, though a trial of thyroid hormone is reasonable if the person has symptoms that seem like they might be from hypothyroidism (like tiredness and feeling cold). 

The second article says that treatment should be considered in any patient with a persistently elevated TSH level, depending on the clinical judgment of the doctor. 

My own tendency is to give thyroid hormone to any patient who has a persistently elevated TSH even if it is not over 10.

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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