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Thyroid UK
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Cortisol test advice wanted

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.)

2 Replies

Hi the Dexamethasone test is to test to see if you may have Cushing's which as you say is high cortisol levels. They are looking to see if you suppress on the blood test, which means that the Dexa suppresses the cortisol production which is what happens with people who don't have Cushing's. If you don't suppress it is a pointer towards Cushing's. However some people with Cushing's will suppress on the test. Your GP could do the 24 hr urine test, some will do saliva but they are usually done by the Endo. What symptoms do you have for them to think of Cushing's?

You shouldn't really notice any changes by taking the Dexa. Has your GP done a 8/9am cortisol blood test & if so what was the result?

I've had Cushing's so know quite a lot about it! If you are on Facebook there is a group called Cushing's UK where you can find out some more information.

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Thanks very much for your reply Pauline. I'm sorry you had Cushing's and hope you are feeling better now. Thanks for the reassurance about the Dexa, it makes me feel better about that aspect.

I don't think I have any symptoms of Cushing's. The endo is only pursuing something other than thyroid because I'm feeling terrible but my thyroid bloods are currently in the infernal 'normal' range. Maybe also because I said there is a circadian element to my symptoms. If anything, I tick off a few Addison's symptoms - but these are ones which are also very 'thyroid'. I spoke to a GP today and asked how will this test help diagnose me if I have low cortisol not high and he couldn't answer that. I presume because it won't!

The reason I am having the dexamethasone at all is because I had a previous 8 am cortisol test last week (result 470 but no range given) but had a very stressful morning so I told the GP I was worried a low cortisol situation would be masked by that and please could I have another test.

Well, the GP wants to see what this second test says and go from there but he forgets that every day I have to feel like this is another horrendous day. I can see what will happen, the test will come back normal and I will have to go back a third time and ask for the urine one!

Thanks again for your reply.


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