Sick euthyroid is seen in unwell patients who are clinically euthyroid but have low levels of T3 and T4. The syndrome is very common and, in fact, may be found in up to 70% of hospitalized patients. This is often why TFT’s are not accurate on patients in ITU.

The rare syndrome of resistance to thyroid hormone (RTH) is an inherited disorder called Refetoff syndrome that involves reduced tissue sensitivity to the thyroid hormone.