In a patient with Cushing's syndrome, what laboratory finding would typically be expected?

In a patient with Cushing's syndrome, the expected laboratory finding is increased 24-hour urinary free cortisol. Cushing's syndrome is characterized by hypercortisolism, which occurs due to excessive cortisol production, whether from endogenous sources like a pituitary adenoma (Cushing's disease), adrenal tumors, or ectopic ACTH secretion.

The measurement of 24-hour urinary free cortisol provides a comprehensive assessment of cortisol secretion over an entire day, and elevated levels are indicative of Cushing's syndrome. This test is considered a reliable method for diagnosing the condition because it reflects the cumulative cortisol output and helps to differentiate between normal and excessive cortisol production.

Other options would not align with the expected findings in Cushing's syndrome. For instance, low 24-hour urinary free cortisol would suggest a normal or decreased cortisol production, which is not consistent with the syndrome. Normal serum ACTH levels can occur in some subtypes of Cushing's syndrome, but they do not provide clear evidence of the condition itself. Finally, decreased serum cortisol contradicts the fundamental nature of Cushing's syndrome, where elevated cortisol levels are a defining feature. Hence, the correct laboratory finding that supports the diagnosis of Cushing's syndrome is indeed the increased 24-hour urinary free