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Thyroid Diseases

Best Thyroid Test For Me After Atrial Fibrillation Incident

02/13/2007

Question:

I had a TSH of 15.9 and a T4 Free of 0.9 at 5:30 a.m. when I was admitted to the hospital with atrial fibrillation and tachycardia (I have a prolapsed mitral valve). One week later my TSH was 4.75 at 6p.m., and a month after that TSH 5.03 and free T4 0.93 at 9a.m.. I am to follow up in 6 months on the TSH, was not and am not on any meds, except now for baby aspirin since the afib incident. Could that high TSH NOT have been an error, and, if it was accurate, could it cause afib? I do have some symptoms of hypothyroidism, such as usually a low pulse and blood pressure. Is free T4 the same as T4? Thank you.

Answer:

Sometimes just being sick enough to land in the hospital is enough to make your thyroid blood tests temporarily abnormal. Given the two normal TSH's after discharge, I think it is reasonable to keep an eye on it at this point rather than committing you to a lifetime of therapy that you may or may not need. In any case it would be a low TSH (indicating excessive T4 levels) that would be associated with atrial fibrillation, so even if you did have hypothyroidism it wouldn't explain the heart problem. The free T4 measures only the active form of thyroid hormone, whereas the T4 measures the active form plus the protein-bound, inactive form. Therefore the free T4 is the better test.

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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