Diagnostic performance of the thirty-four hour dexamethasone suppression test

The performance of the dexamethasone suppression test (DST) in the diagnostic confirmation of endogenous depression was compared according to two times of blood collection—1600 hr on day 2 (usual sample) and 0800 hr on day 3 (34 hr after dexamethasone intake)—in 14 endogenous depressives and in a control group of 17 psychiatric inpatients with other diagnoses. For the day 2 (1600 hr) sample, a 5 μg/dl cortisol concentration represented the best cut-off score, with sensitivity of 57% specificity of 88%, and diagnostic confidence of 80%. For the day 3 (0800 hr) sample, the best cut-off score was 20 μg/dl, with the same sensitivity (57%) but there was a decrease of both specificity (to 76%) and diagnostic confidence (to 67%). The mean cortisol levels were much higher on day 3 than on day 2, suggesting that the inhibitory activity of dexamethasone was no longer present.