Why This Test Is Used
Unlike a single blood cortisol level (which varies throughout the day), 24-hour urine collection captures total cortisol output, providing a more complete picture — useful for diagnosing conditions of cortisol excess (Cushing's syndrome).Symptoms of Cushing's Syndrome (Excess Cortisol)
- Weight gain, particularly central (abdomen) with thin arms/legs
- Round 'moon' face
- 'Buffalo hump' — fat pad at the back of the neck
- Purple stretch marks (striae)
- Easy bruising, thin skin
- High blood pressure and blood sugar
- Muscle weakness
- In women: irregular periods, excess hair growth
Collection Technique
- Discard the first urine of the day (this is from before the 24-hour period)
- Collect ALL urine for the next 24 hours in the container provided
- Include the first urine of the following morning
- Keep the collection refrigerated/cool throughout
- Return to the lab as instructed
Other Tests Used Alongside
| Test | Purpose |
|---|---|
| Late-night salivary cortisol | Cortisol should be low at night — elevated levels suggest Cushing's |
| Low-dose dexamethasone suppression test | Cortisol should suppress with dexamethasone — failure to suppress suggests Cushing's |
| ACTH level | Helps determine the cause (pituitary, adrenal, or ectopic source) |
Complete Collection Is EssentialAn incomplete 24-hour collection (missing urine) will give a falsely low result and may require repeating the test. Set alarms if needed to remember all collections throughout the day and night.
Why might my doctor suspect Cushing's syndrome?
Doctors consider Cushing's syndrome when several suggestive features are present together (central weight gain, purple stretch marks, high blood pressure, muscle weakness), rather than any single symptom alone.
Can medications cause a false positive result?
Yes — many medications, especially steroid creams, inhalers, or injections (even without oral tablets), can cause an elevated cortisol-like picture. Always tell your doctor about all medications, including over-the-counter and topical products.
What happens if my test is abnormal?
Further tests to determine the cause are needed — this might include an ACTH level, pituitary MRI, or adrenal CT scan, guided by an endocrinologist.
Medical Disclaimer: This page is for general education only and does not replace professional medical advice. Always consult a qualified healthcare provider.