Differentiating Euthyroid sick syndrome from other diseases

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]Associate Editor(s)-in-Chief: Akshun Kalia M.B.B.S.[2]

Overview

Euthyroid sick syndrome must be differentiated from other causes of hypothyroidism on the basis of clinical features and laboratory findings. In euthyroid sick syndrome, serum T3 is decreased more than T4, the T3RU (T3 resin uptake) is high, and TSH is normal or mildly decreased. In primary hypothyroidism, serum T4 is decreased more than T3, the T3RU (T3 resin uptake) is low, and TSH is increased. Other causes of hypothyroidism include transient hypothyroidism, sub-clinical hypothyroidism, central hypothyroidism (pituitary or hypothalamic) and peripheral resistance to TSH/TRH.

Differentiating Euthyroid sick syndrome from other Diseases

Euthyroid sick syndrome must be differentiated from other causes of hypothyroidism on the basis of history and symptoms and laboratory findings:

Disease			History and symptoms			Laboratory findings							Additional findings
			Fever	Goiter	Pain	TSH	Free T4	T3	T3RU	Thyroglobin	TRH	TPOAb
Euthyroid sick syndrome		Mild	+	-	-	Normal	Normal	↓	↑	-	Normal	-	Additional findings of underlying condition
		Moderate	+	-	-	Normal /↓	Normal /↓	↓	↑	-	Normal/↓	-
		Severe	+	-	-	↓	N/↓	↓	↑	-	↓	-
Primary hypothyroidism	Autoimmune		+	+/- Diffuse	-	↑	↓	Normal/↓	Normal	Normal/↑	Normal	↑	May be accompanied by other autoimmune diseases
	Thyroiditis		+	+/-	+	↑	↓	Normal	Normal	Normal/↑	Normal	Normal	Infectious thyroiditis associated with neck pain
	Others		-	+/-	-	↑	↓	Normal	Normal	Normal/↑	Normal	Normal	History of hyperthyroidism Drug history
Transient hypothyroidism			+/-	-	+/-	↑	↑	Normal	Normal	↑	Normal	Normal	May present primarily with hyperthyroidism
Subclinical hypothyroidism			-	-	-	↑	Normal	Normal	Normal	↑	Normal	Normal/↑	Asymptomatic
Central Hypothyroidism	Pituitary		+	-	-	Normal/↓	Normal/↓	Normal/↓	↓	Normal	Normal	Normal	Other pituitary hormone deficiencies signs
	Hypothalamus		+	-	-				↑	Normal	↓	Normal	Other pituitary hormone deficiencies signs
Resistance to TSH/TRH			-	-	-	↑	Normal/↓	Normal/↓	Normal	Normal	↑/↓	Normal	Rare