The TRH test at South Tyneside, ‘should it be confined to the dustbin?’
A Jordan, A Basu, JH Parr & ST Wahid
To quantify the reasons for undertaking TRH testing and whether it changed management.
A standard protocol was utilised-normal TSH response is peak 5-20 mUper litre at 20 mins with 60-minute level falling by third off peak. Hospital notes of 53-pts undergoing their first TRH test between October 2000 and May 2004 were reviewed.
44 (83%) pts had the test because of an isolated low free-T4 or symptoms/signs of hypopituitarism with supporting investigations. The test was normal in 33/44 (75%) pts- 2 pts had low basal free-T4 levels and subsequent investigations confirmed idiopathic hypopituitarism and macroadenoma.
5/44 tests were suppressed- no pts had a low basal free-T4 and the final diagnoses were solitary thyroid adenoma 2-pts, idiopathic-hypopituitarism 1-pt, isolated low TSH 1-pt and one non-functioning macroadenoma.
5/44 tests exhibited a hypothalamic response- 2 pts had low basal free-T4s and were diagnosed as a macroprolactinoma and radiotherapy-induced hypopituitarism, 3-pts had normal basal free-T4s of whom 2 had sick-euthyroid syndrome and one an eating disorder.
8-pts had the test to investigate hyperprolactinaemia. None of the prolactins were suppressed. 3-pts had macroprolactinomas, 3 microprolactinomas on MRI and 2 'unseen' microprolactinomas.
TRH testing to investigate hyperprolactinaemia didn't influence clinical management. Our results suggest that the TRH test should not be requested in any isolated abnormality of the thyroid axis in the absence of other clinical clues-other axes (baseline endocrine tests) suggestive of a pituitary disorder or where an eating disorder is being considered in the differential diagnoses of hypopituitarism. Despite National guidance thyroid testing is commonly done as a routine in the community inevitably identifying pts with non-thyroidal illness patterns of TSH/fT4/fT3. Such pts may receive inappropriate treatment and continued monitoring of their thyroid in the community. It could be argued that a normal TRH test may prevent the latter.