From the Guidelines
A 24-hour urine cortisol level of 37 is within the normal range, indicating normal adrenal function. Normal 24-hour urine cortisol typically ranges from 10-100 μg/24h, though reference ranges may vary slightly between laboratories 1. This result suggests that your body is producing appropriate amounts of cortisol, the primary stress hormone that regulates metabolism, immune response, and helps your body respond to stress. No specific treatment or medication is needed for a normal cortisol level. If you were tested due to symptoms suggesting either excess cortisol (Cushing's syndrome) or deficient cortisol (Addison's disease), this result helps rule out these conditions. However, if you continue experiencing symptoms despite this normal result, additional testing might be warranted, as a single normal test doesn't always exclude all possible adrenal disorders. Cortisol levels naturally fluctuate throughout the day, with highest levels typically in the morning and lowest at night, which is why the 24-hour collection provides a more comprehensive assessment than a single blood test. Some key points to consider in the diagnosis and management of Cushing's syndrome include:
- The use of 24-hour urine cortisol collection as a diagnostic tool, with a cut-off value of >193 nmol/24 h (>70 μg/m2) for confirmation of Cushing syndrome 1
- The importance of determining the cause of hypercortisolism, with Cushing disease being the most common cause of ACTH-dependent Cushing syndrome 1
- The role of bilateral inferior petrosal sinus sampling (BSIPSS) in confirming a central source of ACTH excess and lateralizing the tumor 1
- The use of medical management, such as steroidogenesis inhibitors, in the treatment of Cushing's syndrome, particularly in cases where surgery is not possible or has failed 1. It is essential to note that the diagnosis and management of Cushing's syndrome require a comprehensive approach, taking into account the patient's clinical presentation, laboratory results, and imaging studies. In this case, the normal 24-hour urine cortisol level suggests that Cushing's syndrome is unlikely, but further evaluation may be necessary to rule out other adrenal disorders. The most recent and highest quality study, published in 2024, provides guidance on the diagnosis and management of Cushing's syndrome, including the use of 24-hour urine cortisol collection and BSIPSS 1. Overall, the management of Cushing's syndrome requires a multidisciplinary approach, involving endocrinologists, radiologists, and surgeons, to ensure optimal outcomes for patients.
From the Research
24h Urine Cortisol
- A 24h urine cortisol level of 37 is considered low, as normal values typically range from 10-100 μg/24h 2
- This low level may indicate hypocortisolism, which can be primary (adrenal disease, Addison's disease) or secondary (pituitary or hypothalamic disorder) 2
- However, 24h urine cortisol measurement is not an established method for confirming hypocortisolism, as most analytical methods are too unspecific and insensitive in the subnormal range 2
Diagnosis and Treatment
- The diagnosis of Cushing's syndrome (CS) typically involves measurement of 24-hour urinary free cortisol (UFC) and the low-dose dexamethasone suppression test 2
- Treatment for CS often involves steroidogenesis inhibitors, such as metyrapone, ketoconazole, and osilodrostat, which can help reduce hypercortisolism 3, 4, 5, 6
- Combination therapy with mitotane, metyrapone, and ketoconazole has been shown to be effective in severe ACTH-dependent CS 5
Laboratory Measurements
- 24h-UFC determinations by immunoassays (IA) are commonly overestimated due to steroid metabolites' cross-reaction 3
- Gas chromatography-mass spectrometry (GC-MS) is a more accurate method for measuring 24h-UFC, but IA is still widely used due to its convenience and lower cost 3
- The reliability of 24h-UFC IA determinations can be altered by changes in urinary steroid metabolites, such as those induced by ketoconazole and metyrapone treatment 3