Effect of weekly testing on dexamethasone suppression test results in normal subjects.

Four weekly repetitions of the overnight dexamethasone suppression test (DST) in each of 10 healthy volunteers yielded plasma cortisol levels that were consistently suppressed. These results suggest that unlike some dynamic tests of hypothalamic-pituitary functioning, the DST does not produce false-positive results due to weekly repetition. This finding is of interest because previous research has demonstrated that a subgroup of melancholic initial nonsuppressors continue to resist cortisol suppression despite apparent clinical improvement. The present findings do not support the hypothesis that continued nonsuppression in clinically improved patients is an artifact of serial testing.