Brain iodine metabolism
Since the introduction of third generation of the TSH assay methods, TRH test remains only essential for limited domains.
But for some authors, application of immunoradiometric assays combined with TRH test have not sufficiently evaluated as remarked by some authors.
Thyreotroph cell has a potent desiodase and active in normal subject explaining the strong correlation between T4 and TSH.
Interindividual variability of the activity of desiodase enzyme is very possible because of genetic polymorphism.
We have studied prospectively and determined in and homogenous patients population with treated primary hypothyroidism, a real overdosage by an abolished first generation immunoradiometric TSH to TRH and given optimal dosage of levothyroxine during substitutive thyroid hormono-therapy.
Our criterias for TSH reponse to TRH had for lower limite a delta TSH of 4 UI/ml, this is higher than lower level of 1 UI/ml proposed by some authors.
TRH tests as other dynamic assays of anterior pituitary are useful to amplify subtle abnormalities.
A defect in reponse to hypothalamic hormone can be caused by absence or dysfunction of pituitary cells.