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Subclinical hyperthyroidism 

Subclinical hyperthyroidism
Subclinical hyperthyroidism

Jayne A. Franklyn

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date: 18 May 2022

Subclinical hyperthyroidism is defined biochemically as the association of a low serum thyroid-stimulating hormone (TSH) value with normal circulating concentrations of free thyroxine (T4) and free triiodothyronine (T3). The biochemical diagnosis of subclinical hyperthyroidism is dependent upon the use of sensitive assays for TSH able to distinguish normal values found in euthyroid people from reduced values, so our understanding of this topic has accumulated in recent years since such assays became widely available. An expert panel has recently classified patients with subclinical hyperthyroidism into two groups (1): (1) those with low but detectable serum TSH (0.1–0.4 mU/l) and (2) those with undetectable serum TSH (<0.1 mU/l) reflecting the fact that studies of this condition largely divide people into these categories and that the likely consequences reflect the biochemical severity of the condition.

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