How is Cushing’s diagnosed?
The tests used to diagnose Cushing’s are complicated and may take some time; they may also need to be repeated on several occasions. You may have them as an inpatient or an outpatient.
The first tests are to establish that Cushing’s is present. Only if the presence of Cushing’s is established are further tests performed to identify the location of the cause. This is because most people who have the symptoms of weight gain, high blood pressure, diabetes or problems with excess hair do not have Cushing’s, and so establishing is Cushing’s is present is the essential first step.
Tests to check for Cushing’s
To see if you have Cushing’s you will probably be given a tablet called dexamethasone. In people who do not have Cushing’s, taking this tablet will suppress the production of the hormone cortisol.
You may also have a series of blood tests, urine tests and late-night saliva tests. The urine test involves collecting all the urine you pass during 24 hours (for example, between nine o’clock one morning and nine o’clock the next morning). The hospital will provide a special container for this and you will be told how to take accurate and clean samples; tubes for any saliva tests will also be provided.
If these initial tests indicate that Cushing’s is likely, you will then need further tests to find its location. You may be admitted to hospital for these, and it is likely that you may be referred to a hospital where they are very familiar with Cushing’s.
- blood samples taken throughout the day
- a higher dose of dexamethasone
- an injection of corticotrophin releasing hormone (CRH) or desmopressin (DDAVP) which stimulate the pituitary to release ACTH
- measuring ACTH the blood coming from the pituitary gland – inferior petrosal sinus sampling
After the diagnostic tests have been completed your doctor may decide to treat you in the meantime with drugs, such as metyrapone or ketoconazole, to reduce the amount of cortisol produced by your adrenal glands. If so, you may have to spend two or three days in hospital to assess your response to the tablets or attend regularly as an outpatient.
At the end of all these blood tests your arms might be quite bruised, a tendency to bruise easily is typical of Cushing’s.
You will also have your pituitary and/ or body and adrenal glands scanned, using a type of magnetic scan called an MRI scan, or by a form of X-Ray called a CT scan. You may be given an injection during the scan to improve the results. A minority of patients are allergic to this injection, so do tell the specialist if you have asthma or any allergies. The scan does not hurt but the MRI machine can be noisy and it may involve being inside the scanner for around half an hour. If you think this will make you claustrophobic or nervous, tell your GP who may give you something to help you relax.
Another test which may be carried out initially, or possibly during the follow-up to treatment, is a bone mineral density test. This will establish whether you have lost bone density and might be at risk of developing osteoporosis (thinning and brittleness of the bones).