TRH stimulation test

Introduction

Prior to the development of ultrasensitive assays for TSH, the TRH stimulation test was the primary method of confiming primary hyperthyroidism.

Indications

• investigation of central hypothyroidism
• resolving ambiguous thyroid function studies

Clinical significance

• TRH causes a rise in TSH within 5 minutes of IV administration that reaches a peak serum level in 20-30 minutes & returns to baseline in 2-4 hours
• a normal response to administration of 500 ug of TRH is a rise in TSH of 8.5 fold, absent in primary hyperthyroidism & attenuated in hypothyroidism (2.5 +/- 0.4) fold
• TRH also stimulates growth hormone & prolactin release.

Decreases

conditions that may give a blunted response to TRH include:

• central hypothyroidism (pituitary insufficiency)
• renal failure
• Cushing's syndrome
• depression
• euthyrid sick syndrome
• pharmaceutical agents
  • corticosteroids
  • L-dopa
  • large doses of salicylates
  • thyroid hormone therapy (current or recent)

Procedure

• measure baseline TSH
• TRH 200-500 ug is administered IV
• TSH is measured at 20, 30 & 60 minutes after TRH administration

More general terms

• provocative clinical test
• special chemistry test

Additional terms

• thyrotropin-releasing hormone; thyroliberin; protirelin (TRH)