Circadian analysis of plasma cortisol levels before and after dexamethasone administration in depressed patients.

Pituitary-adrenal regulation in healthy subjects and in depressed patients is very dynamic. Interpretation of results of the 1-mg dexamethasone suppression test has usually depended on the result of a single blood cortisol level measurement obtained in the morning or afternoon. We analyzed circulating cortisol concentrations by obtaining blood samples at 20-minute intervals for 24 hours before and after dexamethasone administration in depressed patients. The results illustrate the variability in patterns of escape from the effects of dexamethasone among depressed patients; they also indicate the influence of the sampling time on the test results and thus on the relationship of the test result to various clinical classifications. Finally, these results provide the basis for understanding the consequences of alternative sampling strategies.