American Board of Internal Medicine (ABIM) Certification Practice Exam

How many abnormal first-line screening tests are required to diagnose Cushing syndrome?

1. One

2. Two

3. Three

4. Four

The correct answer is: Two

In the diagnosis of Cushing syndrome, the presence of hypercortisolism must be confirmed through specific screening tests. Clinical guidelines indicate that at least two abnormal first-line screening tests are traditionally required to make a definitive diagnosis. This helps to ensure that the results are consistent and not due to transient factors that might cause a temporary elevation in cortisol levels. The most common first-line tests include the 24-hour urinary free cortisol measurement, late-night salivary cortisol measurement, and the low-dose dexamethasone suppression test. It is essential for two of these tests to yield abnormal results to suggest a diagnosis of Cushing syndrome. Relying on a single test may not provide sufficient evidence of the condition because there can be instances of false positives due to physiological stress, other illnesses, or laboratory errors. Hence, confirming the diagnosis with two abnormal results enhances the accuracy and reliability of the diagnosis.