When TSH is Erratically High
Mar
26
Written by:
3/26/2010
TSH is a pituitary hormone that helps regulate thyroid hormone levels. Normally as soon as thyroid hormone levels start to rise, the pituitary will stop or slow down on TSH release in an effort to prevent hyperthryoidism from developing. In most cases, TSH will fall as low as <.01 mu/L before thyroid hormone levels rise higher than the reference range.
However, if it's a fast rise in thyroid hormone levels, caused by stopping anti-thyroid meds abruptly or exposure to iodine contrast dyes or the heart drug amiodarone, thyroid hormone levels can rise quickly. In these examples, it can TSH a good 6 weeks to catch up and fall low enough to reflect hyperthyroidism.
In resistance to thyroid hormone (RTH) a mutation to the thyroid hormone receptor causes the pituitary to not recognize a rise in thyroid hormone levels. In this case, thyroid hormone levels are high while TSH remains normal or only slightly decreased. Studies show that RTH is often misdiagnosed as Graves' disease. Researchers in New Hampshire describe a case of RTH co-existing with Graves' disease. In this case, after RAI ablation, excessively high doses of replacement hormone were needed to bring TSH within range.