TRH stimulation test

Prior to the development of ultrasensitive assays for TSH, the TRH stimulation test was the primary method of confiming primary hyperthyroidism. Indications: 1) investigation of central hypothyroidism 2) resolving ambiguous thyroid function studies Procedure: 1) measure baseline TSH 2) TRH 200-500 ug is administered IV 3) TSH is measured at 20, 30 & 60 minutes after TRH administration 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: 1) central hypothyroidism (pituitary insufficiency) 2) renal failure 3) Cushing's syndrome 4) depression 5) euthyrid sick syndrome 6) pharmaceutical agents a) corticosteroids b) L-dopa c) large doses of salicylates d) thyroid hormone therapy (current or recent)

General

provocative clinical test special chemistry test

References

Saunders Manual of Medical Practice, Rakel (ed), WB Saunders, Philadelphia, 1996, pg 339-40