• Plasma levels of cortisol were sampled for 24 hours in 32 endogenously depressed (ED) patients and 72 normal controls who also underwent the dexamethasone suppression test. The ED patients had significantly higher mean 24-hour plasma levels of cortisol (X̄ 24h PC). However, X̄ 24h PC values of subjects in both groups were normally distributed, with a marked overlap between the two. Only seven ED patients had X̄ 24h PC values higher than 2 SDs from the normal mean (>10 μg/dL). An abnormal dexamethasone suppression test result was only partially related to basal cortisol levels. The mean plasma level of cortisol between 1 and 4 pm was found to be highly correlated with the X̄ 24h PC value in ED patients, as has been previously reported in normal subjects and patients with various other diseases (in which it also powerfully discriminated between hypersecretors and normosecretors). This finding supports the use of mean cortisol levels between 1 and 4 pm as a reliable and convenient indication of cortisol secretion.
Halbreich U, Asnis GM, Shindledecker R, Zumoff B, Nathan RS. Cortisol Secretion in Endogenous DepressionI. Basal Plasma Levels. Arch Gen Psychiatry. 1985;42(9):904-908. doi:10.1001/archpsyc.1985.01790320076010