Evaluation Of The Low Dose Dexamethasone Suppression Test, Midnight Serum Cortisol And Urinary Free Cortisol In The Diagnosis Of The Cushing’s Syndrome

ObjectiveTo evaluate efficacy of the low dose dexamethasone suppression test(LDDST),midnight serum cortisol(F0) and urinary free cortisol(UFC) in the diagnosis ofCushing’s syndrome, and explore the best diagnostic cut-off value.Methods The clinical data of285patients surgically conformed as Cushing’s syndrome and146patients of pseudo-Cushing’s states in Chinese PLA General Hospital from1991~2011were retrospectively analyzed. ROC curve was used to evaluate efficacy ofthe the low dose dexamethasone suppression test, midnight serum cortisol and urinaryfree cortisol, explore the best cut-off value and its corresponding sensitivity andspecificity.Results1. Among285patients of Cushing’s syndrome,154patients were Cushing’sdisease(54%),96patients were adrenal adenoma(33.7%),16patients wereAIMAH(5.6%),14patients were ectopic ACTH syndrome(4.9%),3patients wereadrenal carcinoma(1.05%),1patients was ectopic adrenal adenoma(0.35%),1patientswas PPNAD(0.35%).146patients of pseudo-Cushing’s states include obesity, primaryhypertension, polycystic ovary syndrome, diabetes mellitus, insulin resistance andsecondary amenorrhea.2. Area under ROC of serum cortisol level after LDDST was larger than serumcortisol’s inhibition, UFC and its inhibition, which indicate serum cortisol level was thebest diagnostic criterion. To calculate the best cutoff value of serum cortisol is146.5nmol/l (5.3μg/dl), corresponding sensitivity97%, specificity98.9%.3. The diagnostic efficacy of serum cortisol at00:00was better than that at08:00or16:00, so was its consistence with pathological results. The best cut off value of serumcortisol at00:00was249nmol/l, with sensitivity95.5%, specificity92.7%.4. UFC was considered as a suitable criterion in the diagnosis of CS. The best cut offvalue of urinary free cortisol was585.5nmol/24h, with sensitivity89.6%, specificity81.7%. Ranking area under ROC of three criteria was LDDST>F0>UFC, so was thediagnostic accuracy. If combine F0and UFC, their diagnostic accuracy was up to98.4%,which was higher than that of LDDST’s accuracy—97.5%. Conclusions1. The best criterion for LDDST in the diagnosis of Cushing’s syndrome was serumcortisol level after LDDST, recommend cutoff point was serum cortisol146.5nmol/l(5.3μg/dl) with both higher sensitivity and specificity. The cutoff point50nmol/l(1.8μg/dl), which was recommended by American Endocrine Society Guideline, paymore attention to sensitivity. The new cutoff point has higher sensitivity at the cost ofspecificity.2. Midnight serum cortisol was better than the other time points’ serum cortisol in thediagnosis of Cushing’s syndrome and consistency with pathological results. Midnightserum cortisol level at249nmol/l has high sensitivity and specificity.3.24h UFC level was an appropriate diagnosis index in Cushing’s syndrome. The bestcut off point of UFC was585.5nmol/24h. LDDST has more diagnostic accuracy than F0and UFC. But combine F0and UFC, their diagnostic accuracy is higher than that ofLDDST.