Dynamics of the cortisol suppression index in depression.

The cortisol suppression index (CSI), a ratio of predexamethasone to postdexamethasone plasma cortisol levels, has been suggested as an alternate approach to the use of the DST in the diagnosis of depression. Forty-eight psychiatric inpatients were prospectively studied to compare the utility of the CSI to results obtained using Carroll's fixed values at 4 p.m. and 11 p.m. Eighty-eight percent (22/25) of depressed patients had an 8 a.m. CSI below 7.0; 73% (16/22) had a 4 p.m. CSI less than 2.5. This compared to a 76% detection rate using Carroll's criteria for nonsuppression. In this study the CSI provided a sensitive and specific interpretation of the dexamethasone suppression test in depression.