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Euthyroid Sick Syndrome


Laura Boucai

, MD, Weill Cornell Medical College

Reviewed/Revised Feb 2024

Euthyroid sick syndrome is a condition in which serum levels of thyroid hormones are low in patients who have nonthyroidal systemic illness but who are actually euthyroid. Diagnosis is based on excluding hypothyroidism. Treatment is directed toward the underlying illness; thyroid hormone replacement is not indicated.

Patients with various acute or chronic nonthyroid disorders may have abnormal thyroid function test results Laboratory Testing of Thyroid Function The thyroid gland, located in the anterior neck just below the cricoid cartilage, consists of 2 lobes connected by an isthmus. Follicular cells in the gland produce the 2 main thyroid hormones... read more . Such disorders include fasting, starvation, protein-energy undernutrition Protein-Energy Undernutrition (PEU) Protein-energy undernutrition (PEU), previously called protein-energy malnutrition, is an energy deficit due to deficiency of all macronutrients, but primarily protein. It commonly includes... read more , severe trauma, myocardial infarction Overview of Acute Coronary Syndromes (ACS) Acute coronary syndromes result from acute obstruction of a coronary artery. Consequences depend on degree and location of obstruction and range from unstable angina to non–ST-segment elevation... read more , chronic kidney disease Chronic Kidney Disease Chronic kidney disease (CKD) is long-standing, progressive deterioration of renal function. Symptoms develop slowly and in advanced stages include anorexia, nausea, vomiting, stomatitis, dysgeusia... read more Chronic Kidney Disease , diabetic ketoacidosis Diabetic Ketoacidosis (DKA) Diabetic ketoacidosis (DKA) is an acute metabolic complication of diabetes characterized by hyperglycemia, hyperketonemia, and metabolic acidosis. Hyperglycemia causes an osmotic diuresis with... read more , anorexia nervosa Anorexia Nervosa Anorexia nervosa is characterized by a relentless pursuit of thinness, a morbid fear of obesity, a distorted body image, and restriction of intake relative to requirements, leading to a significantly... read more , cirrhosis Cirrhosis Cirrhosis is a late stage of hepatic fibrosis that has resulted in widespread distortion of normal hepatic architecture. Cirrhosis is characterized by regenerative nodules surrounded by dense... read more , thermal injury Burns Burns are injuries of skin or other tissue caused by thermal, radiation, chemical, or electrical contact. Burns are classified by depth (superficial and deep partial-thickness, and full-thickness)... read more Burns , drug overdose, and sepsis Sepsis and Septic Shock Sepsis is a clinical syndrome of life-threatening organ dysfunction caused by a dysregulated response to infection. In septic shock, there is critical reduction in tissue perfusion; acute failure... read more .

Decreased triiodothyronine (T3) levels are most common. Patients with more severe or prolonged illness also have decreased thyroxine (T4) levels. Serum reverse T3 (rT3) is increased. Thyroid-stimulating hormone (TSH) levels may be normal or even low, and during the recovery phase of the syndrome TSH levels may be slightly elevated.

Patients are actually euthyroid, but depending upon the underlying acute or chronic condition, may have features that overlap with severe hypothyroidism Hypothyroidism Hypothyroidism is thyroid hormone deficiency. Symptoms include cold intolerance, fatigue, and weight gain. Signs may include a typical facial appearance, hoarse slow speech, and dry skin. Diagnosis... read more Hypothyroidism such as hypothermia, hypoventilation, hypotension, lethargy, or coma.

Pathogenesis is unknown but may include

  • Decreased peripheral conversion of T4 to T3

  • Decreased clearance of rT3 generated from T4

  • Decreased binding of thyroid hormones to thyroxine-binding globulin (TBG)

Proinflammatory cytokines (eg, tumor necrosis factor-alpha, interleukin-1) may be responsible for some changes.

Interpretation of abnormal thyroid function test results in ill patients is complicated by the effects of various medications, including the iodine-rich contrast agents and amiodarone, which impair the peripheral conversion of T4 to T3, and by medications such as dopamine and corticosteroids, which decrease pituitary secretion of TSH, resulting in low serum TSH levels and subsequent decreased T4 secretion.

Pearls & Pitfalls

  • Thyroid function tests should not be ordered for severely ill patients unless thyroid dysfunction is highly suspected.

Diagnosis of Euthyroid Sick Syndrome

  • TSH

  • Serum cortisol

The diagnostic dilemma is whether the patient has hypothyroidism Hypothyroidism Hypothyroidism is thyroid hormone deficiency. Symptoms include cold intolerance, fatigue, and weight gain. Signs may include a typical facial appearance, hoarse slow speech, and dry skin. Diagnosis... read more Hypothyroidism or euthyroid sick syndrome. The best test is measurement of TSH, which in euthyroid sick syndrome is low, normal, or slightly elevated but not as high (usually < 10 mIU/L [10 microIU/mL]) as it would be in primary hypothyroidism (see table ).

Serum rT3 is elevated, although this measurement is rarely done, and the results do not usually return in a time frame to be useful in decision making.

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 test results in patients who are acutely or chronically ill. Unless thyroid dysfunction is highly suspected, thyroid function tests should not be ordered in these patients.

Treatment of Euthyroid Sick Syndrome

  • Treatment of underlying disorder

Treatment with thyroid hormone replacement is not appropriate. When the underlying disorder is treated, results of thyroid tests normalize.

Key Points

  • Many seriously ill patients have low levels of thyroid hormones but are not clinically hypothyroid and do not require thyroid hormone supplementation.

  • Patients with euthyroid sick syndrome have low, normal, or only slightly elevated levels of thyroid-stimulating hormone (TSH), unlike the marked TSH elevations present in true hypothyroidism.

NOTE: This is the Professional Version. CONSUMERS: View Consumer Version
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