Hi, I have a cortisol blood test booked for Wednesday morning and the GP has prescribed a low dose of dexamethasone to be taken at midnight before the test. Apparently this will avoid any stressors in the morning affecting my result. He mentioned this as a test for Cushing's which I think is high cortisol.
But what if I have low cortisol? Is the test useless for that? And if I am low and I am given dexamethasone to suppress cortisol, how will it make me feel? Would it be a bad thing? I am feeling dreadful so I do want the test but don't want to muck my poor body about unnecessarily.
Also, has anyone had a 24 salivary cortisol test or urinary cortisol test ordered by a GP instead of a blood test?
(History: thyrotoxicosis diagnosed in March; went hypo on Carbimazole in April; got back into low 'normal' range in June and felt very well; started feeling very ill again suddenly four weeks ago.)