What is the best screening for Cushing syndrome? What is the best diagnostic test for a patient with suspected Cushing syndrome?

Cushing’s syndrome is a hormonal disorder caused by prolonged exposure to high levels of the hormone cortisol. This can be due to taking glucocorticoid medicines, but it can also be caused by tumors that produce cortisol or adrenocorticotropic hormone (ACTH), which regulates cortisol production.

When it comes to screening for Cushing’s syndrome, the most common tests include late-night salivary cortisol, 24-hour urinary free cortisol, and the low-dose dexamethasone suppression test.

The late-night salivary cortisol test involves collecting a small sample of saliva late at night and measuring the level of cortisol. Normally, cortisol levels drop in the evening, but in people with Cushing’s syndrome, these levels are often elevated.

The 24-hour urinary free cortisol test involves collecting urine over a 24-hour period and measuring the amount of cortisol. Elevated levels of cortisol in the urine can indicate Cushing’s syndrome.

The low-dose dexamethasone suppression test involves taking a low dose of the medication dexamethasone, which normally suppresses cortisol production, and then measuring cortisol levels. In people with Cushing’s syndrome, cortisol levels often do not decrease as expected after taking dexamethasone.

If any of these tests are abnormal, further testing is usually needed to confirm the diagnosis and determine the cause of Cushing’s syndrome. This can include additional blood tests, imaging tests such as CT or MRI scans to look for tumors, and sometimes a test called inferior petrosal sinus sampling, which can help determine if the cause is a pituitary adenoma.

It’s important to note that diagnosing Cushing’s syndrome can be complex and requires a specialist in hormonal diseases, known as an endocrinologist. If Cushing’s syndrome is suspected, it’s crucial to consult with an endocrinologist for a thorough evaluation and appropriate testing.