Sick Euthyroid Syndrome

By Dr Rob Hackett

Abnormal thyroid function tests are common in the ICU. Dr Rob Hackett explains the Sick Euthyroid Syndrome.


Abnormal findings on thyroid function tests that occur in the setting of a nonthyroidal illness, without pre-existing hypothalamic-pituitary and thyroid gland dysfunction

The most prominent alterations are:

Low serum triiodothyronine (T3)

Elevated reverse T3 (rT3)

Thyroid-stimulating hormone (TSH), thyroxine (T4), free T4 (FT4), and free T4 index (FTI) also are affected in variable degrees based on the severity and duration of the NTI.

Serum cortisol is often elevated in euthyroid sick syndrome and low or low-normal in hypothyroidism due to pituitary-hypothalamic disease.

Because tests are nonspecific, clinical judgment is required to interpret abnormal thyroid function tests in the acutely or chronically ill patient

Recommended tests include the following:

Total T4

Total T3


Free T4


Free T3

There is no prospective study to date demonstrating benefit or harm of thyroid hormone replacement in NTI.

Several trials investigated a possible therapy of ESS. However, they yielded inconsistent and partly contradictory results. This may be caused in the fact that the investigated populations were too heterogeneous in the lack of a consistent definition of sick euthyroid.

Thyroid hormones have been used in the setting of NTI in various settings with T4 and T3 replacement and still remain controversial.