New Cut-off Value for Low-Dose Acth Stimulation Test in the Diagnosis of Adrenal Insufficiency

Aim: Although the peak cortisol response in the low-dose test does not reach the generally accepted value of 18 & mu;g/dL, there are many patients whose adrenal insufficiency diagnosis was ruled out by getting an adequate response with the standard-dose test. Thus, the standard-dose adrenocorticotropic hormone (ACTH) stimulation test is unnecessarily applied to many patients. This study aims to compare low- and standard-dose ACTH stimulation tests in diagnosing adrenal insufficiency and to determine a new optimal threshold level for low-dose ACTH stimulation tests to avoid unnecessary standard-dose ACTH tests.Methods: In this single-center cross-sectional study, patients with suspected adrenal insufficiency who underwent low-dose (1 mcg) and standard-dose (250 mcg) ACTH stimulation tests were evaluated. Cases were separated into two groups: (I) inadequate cortisol response (<18 mcg/dL) to low-dose test and adequate response (& GE;18 mcg/dL) to the standard dose, (II) adrenal insufficiency by inadequate responses to both tests. In addition, the cortisol responses to the stimulation tests of the group not diagnosed with adrenal insufficiency and those diagnosed with adrenal insufficiency were compared.Results: Comparing 115 cases' peak cortisol levels, we found that the values of standard-dose tests were statistically significantly higher than those of low-dose tests (p<0.001). According to the receiver operating characteristic analysis we performed to determine a new cut-off level to eliminate adrenal insufficiency in the low-dose test, when the cut-off value was set as 16 & mu;g/dL; 100% sensitivity, 35.64% specificities, 17.72% positive predictive value, and 100% negative predictive value were obtained. It has been shown that this new cut-off value would eliminate the diagnosis of adrenal insufficiency without performing the standard dose test in 36 cases.Conclusion: The need for standard-dose testing can be reduced by lowering the cut-off point of the low-dose test from the accepted adequate cortisol level of 18 mcg/dL to 16 mcg/dL.