Results of Thyroid Function Tests in Various Clinical Situations
Physiologic State | Serum TSH | Serum Free T4 | Serum T3 | 24-hour Radioiodine Uptake |
|---|---|---|---|---|
Untreated | Low* | High | High | High |
T3 toxicosis | Low | Normal | High | Normal or high |
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 |
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. | ||||