low TSH, normal free thyroid hormones

Last reviewed 06/2021

The most common cause of these test results is excessive thyroxine ingestion.

Otherwise the combination of a suppressed TSH and normal free thyroid hormones is usually an asymptomatic disorder termed subclinical hyperthyroidism. In the elderly subclinical hyperthyroidism is often caused by multinodular goitre.

Rare causes of low TSH with normal free thyroid hormones are seen in hospital practice:

  • high dose steroid therapy
  • dopamine and dobutamine infusion
  • other systemic illness

Complete suppression of TSH (<0.1 mU/L) merits treatment for hyperthyroidism because of the significant increased morbidity associated with subclinical hyperthyroidism