ABSTRACT
Cushing's syndrome results from prolonged and excessive exposure to medically prescribed corticosteroids, or from excess endogenous cortisol secretion. When endogenous cortisol secretion is suspected, several screening tests are conducted in order to confirm or to rule out the diagnosis. In recent years, as the cut-off point of cortisol concentration on the 1 mg overnight dexamethasone suppression test was lowered, the prevalence of Cushing's syndrome has increased, and more cases of mild syndromes, with negative results on one or more screening tests, have increasingly been reported. In this paper, we will describe the various screening tests used for Cushing's syndrome, and will discuss their degree of sensitivity in the diagnosis of mild cases. We conclude that, in cases of mild syndromes, the sensitivity of some tests appears to be notably lower than has been reported. Until recently, the major challenge has been to distinguish between pseudo-Cushing's states and Cushing's syndrome. Today, however, the challenge has become to avoid misdiagnosis of mild cases, presenting with normal results on some screening tests. The sensitivity of urinary free cortisol seems to be lower than previously reported. Therefore, we recommend not to rely solely on this test in ruling out Cushing's syndrome.
