A 44-year-old woman with hirsutism, central obesity, and hypertension undergoes a 1 mg overnight dexamethasone suppression test. Morning serum cortisol is 4.5 microgram/dL. What is the correct interpretation?
- A Cushing syndrome is excluded and no further testing is needed
- B The result is abnormal and requires further evaluation for Cushing syndrome ✓
- C The test confirms pituitary-dependent Cushing disease specifically
- D The test should be repeated only if urinary free cortisol is also available
Correct answer: B. The result is abnormal and requires further evaluation for Cushing syndrome
Explanation
Normal suppression after 1 mg overnight dexamethasone requires morning cortisol below approximately 1.8 microgram/dL (50 nmol/L). A value of 4.5 microgram/dL is a positive screen for Cushing syndrome, though false positives occur with obesity, depression, alcohol use, and oestrogen raising CBG. Exogenous oestrogens should be stopped before retesting. The test cannot localise the source, so confirming pituitary disease (option C) requires ACTH levels, high-dose suppression, or pituitary imaging after confirmation.
Reference: Williams Textbook of Endocrinology, 14th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.