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—The Chief editor kindly permitted us the opportunity to comment on Dr Maruta's letter. Dr Maruta, like us, expresses a deep concern about the indiscriminate use of plasma cortisol values for the DST without considering the methods used to obtain the values. Undoubtedly, this has already created a great deal of confusion among psychiatrists who perform the DST for diagnosing endogenous depressions, and use 5 μg/dL as a cutoff point between DST suppressors and nonsuppressors. A cortisol value of 5 μg/dL does not mean the same concentration of steroid, as the quantitation varies among laboratories using different methods.Dr Maruta's argument for "corticosteroid concentration" instead of "true cortisol" has some truth to it, but seems to split hairs. As long as corticosterone, the other major glucocorticoid in human blood, produces the same biological effects as cortisol
Fang VS, Meltzer HY. Dexamethasone Suppression Test: Technique and Accuracy-Reply. Arch Gen Psychiatry. 1982;39(10):1218. doi:10.1001/archpsyc.1982.04290100074014