Results of Thyroid Function Tests in Various Clinical Situations

Physiologic State

Serum TSH

Serum Free T4

Serum T3

24-hour Radioiodine Uptake

Hyperthyroidism

Untreated

Low*

High

High

High

T3 toxicosis

Low

Normal

High

Normal or high

Hypothyroidism

Primary, untreated

High

Low

Low or normal

Low or normal

Secondary to pituitary disease

Low or normal

Low

Low or normal

Low or normal

Euthyroidism

Patient taking iodine

Normal

Normal

Normal

Low

Patient taking exogenous thyroid hormone

Normal or low

Normal in patient taking T4, low in patient taking T3

High in patient taking T3, normal in patient taking T4

Low

Patient taking estrogen

Normal

Normal

High

Normal

Euthyroid sick syndrome

Normal, low, or high

Normal or low

Low

Normal

* TSH is low in patients with hyperthyroidism except in the rare instance when the etiology is a TSH-secreting pituitary adenoma or pituitary resistance to the normal inhibition by thyroid hormone.

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