Key Information

Appropriate Tests

Sick euthyroid syndrome

The interpretation of thyroid function tests in an acutely ill patient is difficult and the tests should generally be reserved for when there is clinical suspicion of myxoedema coma or thyroid crisis.

Thyroid stimulating hormone levels are variable and thyroxine (free) may be low; these findings are seldom of clinical significance.

Thyroid status should be assessed when the patient is otherwise well.


  • Phenytoin
  • Diazepam

The effect is seen only when thyroxine (total) is measured, and is of no clinical significance.

Free T4 is normal.

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