Think twice before ordering thyroid function tests in hospitalized patients

I was asked to see in consultation a 77-year-old woman who had been admitted two days earlier with a pulmonary embolus. The consultation request stated that she had a multinodular goiter and suppressed thyroid-stimulating hormone at 0.13 mIU/L (reference interval 0.34 to 5.60). She provided no history of symptoms that might be associated with hyperthyroidism but this is not unusual or unexpected in this age group. (We can discuss hyperthyroidism in the elderly in another blog.)

The thyroid gland was barely palpable and there were no findings on examination consistent with hyperthyroidism aside from mild tachycardia at 88 beats per minute. Repeat thyroid tests were free T4 1.05 ng/mL (reference interval 0.5 to 1.5) and TSH 0.85 mIU/L.

This patient had the euthyroid sick syndrome also known as the sick euthyroid syndrome. This is such a common finding in sick hospitalized patients that a case should be made for not ordering thyroid function tests in any hospitalized patient unless the patient has known thyroid disease or there is very compelling evidence that the patient may have hyper- or hypothyroidism.

The patient I saw only had TSH measured. Would things have been different if free T4 or T3 had been measured at the first blood draw? Most likely not! The precise etiology of the abnormal thyroid studies is unclear but it appears to involve down regulation of TSH secretion and shunting of T4 metabolism towards reverse T3. However, almost any pattern of abnormal thyroid function tests has been observed in the euthyroid sick syndrome such that no combination of results would come as a surprise.

This observation seems to hold true even for patients admitted with new onset atrial fibrillation in whom the finding of previously unrecognized hyperthyroidism is uncommon when the only clinical feature is atrial fibrillation. While I can make a strong case for not ordering thyroid function tests in my patient with a pulmonary embolus or other conditions requiring hospitalization, I need to soften my position for now with atrial fibrillation patients. Just be sure to interpret the results with care.