Table 1. Diagnostic studies.

Diagnostic studies	No.	%
Absent diurnal cortisol rhythma	29/29	100
Failure to cortisol suppression by low dose dexamethasone	18/22	82
Cortisol suppression by high dose dexamethasoneb	23/27	85
Highc 24-h urine free cortisol	21/23	91.3

^aMeans of 2 serum cortisol values obtained at 0730–0800H and at 0000–0030H

The presence of diurnal cortisol rhythm defined when serum cortisol concentration reached its zenith in the morning (06.00–08.00 h) and its nadir in the night during the first half of normal sleep [2]

^bCortisol reduced from baseline by ≥50%

^cMore than 80 μg/m2 [2]