What causes a low TSH level with a normal free T4 level?

Abstract

Subclinical hyperthyroidism (SCH) is defined as a low thyroid-stimulating hormone (TSH) level with normal free T4 and free T3 levels in patients without specific symptoms of hyperthyroidism. There is no evidence that treating SCH results in improved cardiovascular outcomes and evidence is insufficient that it improves neuropsychiatric outcomes (strength of recommendation [SOR]: C). Bone mineral density may be increased with treatment of SCH (SOR: B, based on one randomized clinical trial).