Background and aim

Dexamethasone Suppression Test (DST), recommended for Cushing’s Syndrome (CS) diagnosis, explores the pituitary feedback to glucocorticoids. Its diagnostic accuracy could be affected by dexamethasone bioavailability, and therefore, we have developed and validated a dexamethasone threshold after 1-mg DST.

Materials and methods

We studied 200 subjects: 125 patients were considered retrospectively and 75 were enrolled prospectively as the validation cohort. Serum dexamethasone, Late Night Salivary Cortisol (LNSC), and Urinary Free Cortisol (UFC) were measured with LC–MS/MS. Normal LNSC and UFC levels were used to exclude CS. The lower 2.5th percentile of dexamethasone distribution in non-CS patients with cortisol ≤ 50 nmol/L after 1-mg DST was used as threshold.

Results

16 patients were CS and 184 non-CS (108 adrenal incidentaloma and 76 excluded CS); 4.5 nmol/L resulted the calculated threshold. Cortisol after 1-mg DST confirmed high sensitivity (100% at 50 nmol/L cut-off) and moderate–low specificity (63%, increased to 91% at 138 nmol/L) to diagnose CS in the whole cohort of patients. We could reduce the number of false-positive results (from 10 to 6 and from 7 to 4 in AI and excluded CS) considering adequate dexamethasone levels. Dexamethasone levels were not affected by hypercortisolism, age, gender, smoke, weight, and creatinine. 6% of non-CS patients did not achieve adequate dexamethasone levels (40% of tests with serum cortisol > 138 nmol/L after 1-mg DST).

Conclusions

We developed and validated the routine dexamethasone measurement during 1-mg DST: it is independent from patient’s clinical presentation, and it should be used to increase the specificity of serum cortisol levels.

中文翻译：

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低剂量抑制试验中的地塞米松可疑高皮质醇血症测量：阈值发展并通过验证。

背景和目标

推荐用于库欣综合征（CS）诊断的地塞米松抑制试验（DST）探索对糖皮质激素的垂体反馈。地塞米松的生物利用度可能会影响其诊断准确性，因此，我们开发并验证了1 mg DST后的地塞米松阈值。

材料和方法

我们研究了200名受试者：回顾性地考虑了125名患者，前瞻性纳入了75名患者作为验证队列。血清地塞米松，深夜唾液皮质醇（LNSC）和尿液游离皮质醇（UFC）用LC–MS / MS测定。正常的LNSC和UFC水平用于排除CS。在1 mg DST后皮质醇≤50 nmol / L的非CS患者中，地塞米松分布的较低2.5％百分数用作阈值。

结果

CS患者16例，非CS患者184例（肾上腺偶发瘤108例，排除CS的患者76例）；4.5 nmol / L得出计算的阈值。1 mg DST后的皮质醇证实在整个患者队列中诊断CS的敏感性高（在50 nmol / L截止时为100％）和中低特异性（63％，在138 nmol / L时增加至91％）。考虑到足够的地塞米松水平，我们可以减少假阳性结果的数量（AI和排除CS的假阳性结果从10减少到6，AI从7减少到4）。地塞米松水平不受皮质醇过多症，年龄，性别，吸烟，体重和肌酐的影响。6％的非CS患者未达到适当的地塞米松水平（1 mg DST后40％的血清皮质醇> 138 nmol / L）。

结论

我们开发并验证了在1毫克DST期间的常规地塞米松测量方法：该方法独立于患者的临床表现，应用于提高血清皮质醇水平的特异性。