Hyperthyroidism Diagnosis and Treatment

Laboratory Findings

In hyperthyroidism, T4 levels are typically elevated above the normal reference range (>22 pmol/L or >10.3 mcg/dL), though the degree of elevation varies depending on the underlying cause and type of hyperthyroidism 1, 2
The classic presentation of overt hyperthyroidism shows suppressed TSH (<0.45 mIU/L, often <0.1 mIU/L or undetectable) 1, 2, 3
Elevated free T4 above the upper limit of normal (typically >22 pmol/L) is a characteristic finding in overt hyperthyroidism 1, 2

A single abnormal T4 measurement is insufficient for diagnosis, and multiple tests over a 3-6 month interval are required to confirm persistently abnormal findings 1, 3
Follow-up T4 testing in patients with persistently low TSH differentiates subclinical hyperthyroidism (normal T4) from overt hyperthyroidism (elevated T4) 1, 3

Treatment decisions are based on TSH suppression severity, with treatment generally recommended for TSH <0.1 mIU/L with elevated T4, particularly with overt Graves' disease or nodular thyroid disease 1, 3
For subclinical hyperthyroidism (TSH 0.1-0.45 mIU/L with normal T4), treatment is typically not recommended, especially when thyroiditis is the cause 1, 3