Thyroid Function in Critically Ill Patients

Mechanisms of TSH Suppression

• Dopamine decreases serum concentrations of all anterior pituitary hormones, including thyroid-stimulating hormone, via D receptors in the anterior pituitary 1, 2
• Dopamine can induce or aggravate low-T3 syndrome by suppressing TSH secretion and decreasing thyroxine and tri-iodothyronine levels 1, 2

Clinical Implications for TSH Interpretation

• Do not diagnose hypothyroidism based on TSH alone during acute illness, as TSH suppression is a normal physiological response to critical illness 3
• Do not initiate thyroid hormone treatment based on abnormal TSH alone in critically ill patients, as suppression is typically illness-induced rather than indicating true hypothyroidism 3
• Recheck TSH and free T4 after 3-6 weeks of recovery from acute illness to distinguish between illness-induced suppression and true thyroid disease, as 30-60% of abnormal TSH levels normalize on repeat testing 3