Cortisol, 24-Hour Urine, Following 500 mcg Dexamethasone Suppression, Serum or Plasma, Substance Concentration
This test measures the amount of cortisol in a 24-hour urine collection after a low dose (500 micrograms) of dexamethasone is given. It helps check whether the adrenal glands are producing too much cortisol.
["A low-dose dexamethasone suppression test with 24-hour urine cortisol helps screen for cortisol excess (Cushing syndrome)."]
Key facts at a glance
- LOINC
- 14677-9
- Short code
- Cortis 24h p 500 ug Dex SerPl-sCnc
- Synonyms
- Cortis 24h p 500 ug Dex SerPl-sCnc
- Category
- hormone
- Sample
- serum
- Container
- Red-top tube (SST)
- Units
- N/A
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- Specimen volume
- 5 mL
- Stability
- Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
- Hemolysis max
- 500
- Lipemia max
- 1000
- Icterus max
- 500
- TAT
- 4–24 hours
- Order
- routine
What This Test Measures
Cortisol is a hormone made by the adrenal glands that helps regulate metabolism, blood pressure, and the body's response to stress. Normally, cortisol levels fall when a synthetic steroid such as dexamethasone is given. This test measures total cortisol collected in urine over a full 24 hours after a 500 microgram dose of dexamethasone.
How the Test Is Done
You will be instructed to take a low dose of dexamethasone (500 micrograms) at a scheduled time, often in the evening. You then collect all urine produced over the next 24 hours in a special container provided by the laboratory. The urine sample is sent to the lab, where the cortisol concentration is measured.
Preparing for the Test
Follow your healthcare provider's instructions about timing the dexamethasone dose and starting the urine collection. Tell your provider about all medicines, supplements, and hormones you take, because some can affect cortisol results. Avoid excessive physical stress or illness around the test time unless your provider says otherwise.
What the Results Mean
Results are interpreted by your healthcare provider alongside your symptoms and other tests. In general, cortisol that remains elevated after dexamethasone may suggest excess cortisol production, while a normal suppression response is reassuring. Your provider will explain what your specific result means for you.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
This test is used to evaluate suspected Cushing syndrome, a condition of cortisol excess. It combines a low-dose dexamethasone challenge with a 24-hour urine cortisol measurement to assess whether cortisol production appropriately suppresses. Results should always be interpreted by a clinician in the context of symptoms, medications, and other hormone tests; this test does not by itself establish a diagnosis.
Short name
24-hr Urine Cortisol after 500 mcg Dexamethasone
Frequently asked questions
Do I need to collect every drop of urine for 24 hours?
Should I stop my medications before this test?
Can this test diagnose Cushing syndrome on its own?
Sources
- 1
- 2Lab Tests OnlineSource
- 3
Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.
This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.
This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.
If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.
Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy