Overnight 1 mg dexamethasone suppression test and 24 h urine free cortisol-accuracy and pitfalls when screening for Cushing's syndrome.

Diagnosis of Cushing's syndrome (CS) is often delayed due to variable clinical features and its rarity. Simple and accurate screening tests are required to enhance screening for hypercortisolism. Both overnight 1 mg dexamethasone suppression test (DST) and urinary free cortisol (UFC) demonstrate high sensitivity and specificity for the diagnosis of CS. However, each test has its own distinctive features, making it preferable in specific clinical conditions. This review will discuss the pitfalls for each of those tests.