Euthyroid-Sick Syndrome

50% of patients in ICU may have low T3, T4 or TSH.  These patients were previously thought to be “euthyroid,” and were thought to have euthyroid-sick syndrome.  However, there is evidence that these patients may have acquired transient central thyroid dysfunction.
How to interpret TSH:
  • low but detectable (0.05 to 0.3 mU/L) – will be euthyroid when reassessed after recovery
  • undetectable (<0.01 mU/L) – 75% have hyperthyroidism
  • high (up to 20 mU/L) – some hospitalized patients have transient elevations during recovery from nonthyroidal illness, few have hypothyroidismw hen re-evaluated after recovery
  • very high (>20 mU/L) usually have permanent hypothyroidism

Graph below shows changes in thyroid function tests in nonthyroidal illness.

Thyroid function tests should not be measured on critically ill patients, unless thyroid dysfunction is suspected.  When thyroid dysfunction is suspected, TSH is inadequate and all methods of assessing free T4 are unreliable in severe critical illness.

Patients who are critically ill with low T3 and T4 and no other clinical signs of hypothyroidism should not be treated with thyroid hormone replacement.  Start thyroid replacement if there is evidence of hypothyroidism; in the absence of myxedema coma, start at half the expected full replacement dose.

TREATMENT:  No benefit with hormone replacement.
TAKE HOME:  Thyroid function should not be checked in critically ill patients unless you have a strong suspicion for thryoidal illness.


“Thyroid Function In Nonthyroidal Illness”. N.p., 2016. 14 June 2016.

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