Actualité des investigations biologiques pour le diagnostic du syndrome de Cushing

The demonstration of cortisol overproduction and the determination of its cause are still challenging in spite of the progress in imaging studies performances and in techniques for cortisol overproduction demonstration. The latter is established with the 24-hour urinary free cortisol determination, the best screening test when the threshold is settled at 180 μg/24 h. But, since cortisol overproduction is sometimes periodic in true Cushing's disease, two to three determinations might be necessary for the diagnosis. If 24-hour urine collection cannot be adequately obtained, measurement of salivary cortisol is a good alternative. Overnight dexamethasone test is a good screening test for the exclusion of Cushing's syndrome. Though, false negative and false positive results are frequent. Then, in many cases, the standard dexamethasone test is useful. When cortisol overproduction is established, ACTH determination and high dose dexamethasone test usually lead to the etiological diagnosis.