Patterns of thyroid function tests: Hyperthyroidism

Serum TSH	Serum free T4	Serum T3	Assessment
Normal	Normal	Normal	Euthyroid
Normal hypothalamic-pituitary function
Low	High (or normal)	High	Hyperthyroidism
	Normal	High	T3 toxicosis
	High	Normal	T4 toxicosis
Low	Normal	Normal	Subclinical hyperthyroidism*
Abnormal hypothalamic-pituitary function
Normal or high	High	High	TSH-mediated hyperthyroidism
Low^¶	Normal	Low or normal	Euthyroid with nonthyroidal illness or hyperthyroidism in a critically ill patient. Consider hyperthyroidism in a critically ill patient when TSH is lower^¶ and free T4 and T3 are higher than expected in nonthyroidal illness*.

Thyroid tests must be interpreted in conjunction with clinical presentation.

TSH: thyroid-stimulating hormone; T4: thyroxine; T3: triiodothyronine.

* Euthyroid patients with nonthyroidal illness may have low serum TSH and low-normal or low free T4; T3 is usually low. Some patients with central hypothyroidism have low serum TSH and normal (but usually low-normal) or low free T4 and T3 concentrations.

¶ In critically ill hyperthyroid patients, the TSH is typically very low (eg, <0.01 mU/L). In contrast, detectable but subnormal TSH values (eg, 0.1 to 0.4 mU/L) are more consistent with nonthyroidal illness.

Graphic 142425 Version 1.0

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Patterns of thyroid function tests: Hyperthyroidism