Family Nurse Practitioner Exam

What laboratory finding would support a diagnosis of Cushing's syndrome?

1. Hyponatremia

2. Hypoglycemia

3. Elevated serum cortisol levels

4. Decreased urine 17-ketosteroids

The correct answer is: Elevated serum cortisol levels

When diagnosing Cushing's syndrome, elevated serum cortisol levels are a key laboratory finding that provides strong support for the diagnosis. Cushing's syndrome, characterized by excessive cortisol production, can arise from various causes including pituitary adenomas, adrenal tumors, or ectopic ACTH production. The presence of high cortisol levels in serum is pivotal because cortisol plays a crucial role in glucose metabolism, blood pressure regulation, and the body's stress response. In healthy individuals, cortisol levels typically follow a diurnal rhythm, with higher levels in the morning and lower levels at night. In Cushing's syndrome, this normal rhythm is disrupted, often leading to consistently high levels of cortisol regardless of the time of day. Other laboratory findings can be associated with Cushing's syndrome, but they are not definitive for diagnosis. Hyponatremia, for instance, may occur in other conditions and is not classical for Cushing's syndrome. Similarly, hypoglycemia is not typically seen in this syndrome, as increased cortisol usually leads to higher blood glucose levels. Decreased urine 17-ketosteroids, while relevant for certain adrenal conditions, does not indicate Cushing's syndrome specifically. In summary, the identification of elevated serum cortisol levels aligns clearly with the pathophysiology