A 26-year-old woman has experienced a 7-kg (1 5-Ib) weight gain, mostly in her trunk, and has had increased fat accumulation in her face over the past 6 months. She has also noted gradually progressive acne, hirsutism, weakness, easy bruising, and abdominal stretch marks and has developed oligomenorrhea.
On physical examination, the patient is 160 cm (63 in) tall and weighs 67 kg (147 Ib). Blood pressure is 130/96mm Hg. She has central obesity, acne on her face and trunk, facial hirsutism, and violaceous striae on her lower abdomen.
What is the best test to screen for Cushing’s syndrome in this patient?
A. Morning serum cortisol level
B. Plasma adrenocorticotropin (ACTH) level
C. 1-mg overnight dexamethasone suppression test
D. 8-mg overnight dexamethasone suppression test
E. 24-hour urinary free cortisol measurement

The correct answer is E
Educational Objectives
Identify the appropriate screening test in patients in whom Cushings syndrome is suspected.
The 24-hour urinary free cortisol measurement is the best screening test for Cushings syndrome. The 1-mg overnight dexamethasone suppression test may also be used to screen for this condition, but has a lower degree of accuracy. Serum cortisol and plasma ACTH levels are unreliable because of their marked fluctuations throughout the day. The 8-mg overnight dexamethasone suppression is not a screening test but is useful for determining the cause of Cushings syndrome after the condition has been diagnosed.