Resumo

PARDES, Ester et al. The Overnight 1mg Dexamethasone Test in Healthy Subjects with Normal Weight, Overweight and Obesity: a Multicentric Study. Rev. argent. endocrinol. metab. [online]. 2007, vol.44, n.2, pp.78-85. ISSN 1851-3034.

The overnight oral dexamethasone test assesses the normal negative feedback of cortisol on the hypothalamic-pituitary-adrenal axis (H-P-A) ¹. It is widely used in the screening of Cushing’s Syndrome (CS) ^3,4,5. But the cut-off values for the normal response remains controversial: originally it was considered as 5 ug/dl and in the last years it was reported as 1.8 ug/dl 4. Likewise, there is no agreement about the suppression values in obesity, where a hyperactivity of the H-P-A axis has been reported. Therefore, the Adrenal Department of the Argentine Society of Endocrinology and Metabolism (SAEM) studied 80 healthy subjects recruited from ten hospitals of Buenos Aires in order to assess the normal response in our population. Sixteen women and twenty men, aged 15-66 years old (X = 39.2ys), were classified into three groups, according to their body mass index (BMI): normal weight, BMI- 19-24.9 kg/m2 (n= 39); overweight, BMI- 25-29.9 kg/m² (n=21) and obese subjects, BMI> 30 kg/m² (n=20). They had to be euthyroid and free of corticosteroid treatment, contraceptive pills, hormone replacement therapy, rifampicin and psychotropic drugs at the time of the study. Subjects referring drug abuse, alcoholism, depression, cardiovascular, and renal disorders and,obviously, adrenal diseases were excluded from the study. Dexamethasone 1mg per os was administered at 11p.m. and blood was withdrawn at 8 a.m. on the next morning to determine plasma cortisol concentration. Determinations were centralized in one laboratory and the RIA-DSL (Diagnostic System Laboratories-radioimmunoassay) was used. Additionally, in ten subjects plasma cortisol was also determined in the same blood samples by another radioimmunoassay kit, RIA-DPC (Diagnostic Products Corporation). The Kruskall-Dunn test was used to compare the plasma cortisol levels post-1mg dexamethasone among the three groups studied. In the 10 patients whose determinations were made in the same blood samples by two different RIA-kits (DSL and DPC),the Wilcoxon test was used to compare the results of plasma cortisol between RIA-DSL and RIA-DPC. Results: The results are expressed as X ± SD ug/dl (range). Plasma cortisol levels after 1mg-dexamethasone were: 2.10 ± 0.77 ug/dl ( 0.78- 3.40 ug/dl) in the normal weight goup; 1.94 ± 0.66 ug/dl (0.96-2.90) in the overweight group and 1.86 ± 0.63 ug/dl (0.85-3.30) in the obese subjects (Table I); no significant differences were observed among the three groups (p=0.319). According to these results, the cut-off value for plasma cortisol post-dexamethasone in the normal weight subjects was considered as = 3.4 ug/dl (93.8 nmol/L) using RIA-DSL. Similar suppression values were obtained in the overweight and obese subjects - 2.9 and 3.3 ug/dl, respectively. No false positive results were observed, either individually or in each group (Fig 1). In the 10 subjects whose blood cortisol was simultaneously determined in the same samples by RIA-DSL and RIA-DPC, the median for plasma cortisol was 2.2 ug/dl for the first and 0.5 ug/dl for the latter, respectively, with a significant difference between both RIA kits (p=0.002). (Table II). Conclusions: In this first stage, the present multicentric study shows that a plasma cortisol level post - 1mg dexamethasone suppression of = 3.4 ug/dl ( 93.8 nmol/L) defines our normal population response, with no significant differences among normal weight,overweight and obese subjects. Furthermore, we wish to point out that the cortisol values must be referred to the method and commercial kits used in each laboratory, since significant differences can be observed in the same blood samples when different kits are used, such as we and other authors have observed. We wish to remark the importance of our study, which is the first in its characteristics in Argentina. Furthermore, in a second stage, we plan to enlarge the sample number and to determine blood cortisol in the same samples by using different methods, in order to obtain a standardized cortisol suppression level. We also plan to study patients with confirmed CS and pseudocushing states in order to assess the sensitivity and specificity of the 1mg-dexamethasone suppression test in our population.

Palavras-chave : 1 mg dexamethasone; Test Nugent; Normal suppression; Obesity; Response hypothamic; Pituitary adrenal axis.

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