Euthyroid sick syndrome

Background

Refers to abnormal thyroid function tests in the context of systemic non-thyroidal illness, surgery, or fasting
Transient abnormalities of thyroid function tests are seen in many hospitalized patients
May be classified as
- Low T3 syndrome
- Low T3/low T4 syndrome
- High T4 syndrome
- Other abnormalities

Admitted to hospital for non-thyroidal illness or surgery
- Most common in patients with severe illness
Thyroid function tests are abnormal
- Most commonly low free T3 with normal free T4 and TSH (70% of hospitalized patients)
- Low T3 and low T4 is seen in severely or critically ill patients and portends a poor prognosis
  - One mechanism is decreased TSH in response to corticosteroids and dopamine
- High total T4 is seen in patients with elevated TBG, as seen in chronic hepatitis, primary biliary cirrhosis, and acute intermittent porphyria
- High free and total T4 may be seen in patients treated with amiodarone or given CT contrast agents
- Treatment with heparin can cause a false laboratory measurement of elevated free T4