From the Guidelines
To evaluate for Cushing's syndrome during a secondary hypertension workup, I recommend starting with a 24-hour urinary free cortisol measurement or a low-dose dexamethasone suppression test, as suggested by the 2024 ESC guidelines for the management of elevated blood pressure and hypertension 1. When considering the diagnosis of Cushing's syndrome, it's crucial to prioritize tests that can accurately identify excess cortisol production. The following labs should be included to check for Cushing's syndrome:
- 24-hour urinary free cortisol measurement
- Low-dose dexamethasone suppression test These tests are essential for assessing cortisol secretory status and can help diagnose Cushing's syndrome, which is a critical step in managing secondary hypertension. According to the consensus on diagnosis and management of Cushing's disease, a guideline update published in The Lancet Diabetes and Endocrinology in 2021, the sensitivity of these tests is above 90%, with the highest rates seen with the dexamethasone suppression test and the lowest with urinary free cortisol 1. It's also important to note that if any screening test is positive, confirmation with a second test is recommended, and for patients with confirmed hypercortisolism, additional tests to determine the cause include plasma ACTH levels, a high-dose dexamethasone suppression test, and imaging studies such as pituitary MRI or adrenal CT scan 1. By prioritizing these tests and following the recommended diagnostic algorithm, clinicians can effectively evaluate for Cushing's syndrome and develop an appropriate management plan to improve patient outcomes.
From the Research
Labs to Check for Cushing's Syndrome
To check for Cushing's syndrome in a secondary hypertension workup, the following labs can be included:
- 1-mg dexamethasone suppression test (DST) 2, 3, 4, 5
- Late-night salivary cortisol (LNSC) measurement 2, 6, 3, 4, 5
- 24-hour urinary free cortisol (UFC) excretion 2, 6, 3, 4, 5
- Scalp-hair cortisol/cortisone analysis to assess long-term glucocorticoid exposure 3
- Plasma ACTH concentrations to differentiate between ACTH-dependent and ACTH-independent causes of Cushing's syndrome 3
Considerations for Lab Selection
When selecting labs to check for Cushing's syndrome, consider the following:
- The Endocrine Society's Clinical Practice Guidelines recommend a single test with high diagnostic accuracy, such as 1-mg DST, LNSC, or 24-hour UFC 4
- LNSC may be the most discriminatory test, but its availability should be considered 5
- 1-mg DST is recommended as the screening test for hypertensive patients with an adrenal incidentaloma 5
- UFC levels can reflect the integrated tissue exposure to free cortisol over 24 hours and provide a picture of endogenous hypercortisolism 4