Cortisol after overnight dexamethasone
What this test measures
In this test a small amount of the steroid dexamethasone is taken at night and cortisol is measured the next morning. In most people the steroid switches cortisol production off, so a low value is the expected result.
Why doctors request it
The usual first screening test when cortisol excess (Cushing's syndrome) is being considered.
What commonly pushes it up
- Cortisol excess from any cause
- Failure to absorb or fast breakdown of the dexamethasone, for example with some anti-epilepsy medicines as a class
- Oestrogen-containing contraception, which raises the bound fraction
- Severe stress, depression or alcohol excess
What commonly pushes it down
- The expected result is a suppressed value
Everyday reasons for a value outside the range
- Oestrogen-containing contraception is the commonest reason for a false positive
- Sleep disturbance and shift work affect it
About the sample
Dexamethasone at 11pm, blood at 8 to 9am.
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Read my report freeThis is an educational summary of results you uploaded. It is not medical advice, a diagnosis or a treatment plan, and it does not replace the doctor who requested the test. If you are worried, or a result is marked outside range, discuss it with your doctor. Written and reviewed by a UK consultant physician. Reference ranges vary between laboratories.