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Discriminatory Value of Low-Dose Dexamethasone Suppression Test in Establishing the Diagnosis and Differential Diagnosis of Cushing’s Syndrome

Institute of Endocrinology, 11000 Belgrade, Serbia

Address correspondence to: Milos Zarkovic, Institute of Endocrinology, Dr. Subotica 13, 11000 Belgrade, Serbia. E-mail: mzarkov{at}eunet.yu.

To the editor:

In their recent article in JCEM, Isidori et al. (1) assessed the value of the dexamethasone suppression test (DST) in the diagnosis and differential diagnosis of Cushing’s syndrome. Data were collected between 1964 and 2001, and hormonal assays were performed using three different methodologies. Based on these data, it can be concluded that DST is not dependent on the assay used to determine cortisol. However, in a study by Clark et al. (2), basal and ACTH-stimulated cortisol concentrations were significantly different when determined by different assays, although assays were of the same generation. If there is assay independence of measurable cortisol concentrations during DST, that would allow worldwide standardization of this important test. However, the limit of the assay for cortisol using the fluorometric method is 150 nmol/liter, compared with 50 nmol/liter for the other two assays. The difference could influence both sensitivity and specificity of the DST using combined data. In addition, only one sentence is devoted to the equivalence of RIA and immunoassay, and it seems that validation was done in vitro only (1). We believe that further clarification of this point would be of great significance for diagnostic endocrinology.

Received December 10, 2003.

References

1. Isidori AM, Kaltsas GA, Mohammed S, Morris DG, Jenkins P, Chew SL, Monson JP, Besser GM, Grossman AB 2003 Discriminatory value of low-dose dexamethasone suppression test in establishing the diagnosis and differential diagnosis of Cushing’s syndrome. J Clin Endocrinol Metab 88:5299–5306[Abstract/Free Full Text]
2. Clark PM, Neylon I, Raggatt PR, Sheppard MC, Stewart PM 1998 Defining the normal cortisol response to the short Synacthen test: implications for the investigation of hypothalamic-pituitary disorders. Clin Endocrinol (Oxf) 49:287–292[CrossRef][Medline]

This article has been cited by other articles:

				A. M. Isidori, J. P. Monson, G. M. Besser, and A. B. Grossman Authors' Response: Discriminatory Value of Low-Dose Dexamethasone Suppression Test in Establishing the Diagnosis and Differential Diagnosis of Cushing's Syndrome J. Clin. Endocrinol. Metab., March 1, 2004; 89(3): 1486 - 1486. [Full Text] [PDF]

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