The ACTH stimulation test is used to diagnose adrenal insufficiency (AI). This study evaluated the diagnostic performance of serum delta cortisol from ACTH stimulation tests and determined appropriate cut-off levels of serum 30-minute delta cortisol for the diagnosis of AI, allowing a reduction in the number of 60-minute cortisol tests. A 6-year retrospective study in 471 patients was conducted. The performance of the serum delta cortisol in diagnosing AI was assessd using a multivariable logistic regression model and the area under ROC curves (AuROC). Both serum 30-minute and 60-minute delta cortisol demonstrated equally high diagnostic accuracy for AI (AuROC for LDT : 0.91 vs 0.90 ; HDT : 0.91 vs 0.92, respectively). The 30-minute delta cortisol test was chosen to develop proposed diagnostic cut-off levels due to its simplicity. The proposed lower cut-off level for 30-minute delta cortisol was Δ < 1.8 µg/dL for both LDT and HDT. The upper cut-off levels were Δ > 11.8 µg/dL for LDT and Δ > 10.5 µg/dL for HDT. These cut-off levels yielded high sensitivity and specificity > 90%. The 30-minute serum delta cortisol using the proposed cut-off levels provides diagnostic performance for AI equal to that of the 60-minute test and is more convenient, requires less time, less invasive and is cost-saving. 67 : 95-101, February, 2020.
Keywords: ACTH stimulation test; adrenal insufficiency; serum delta cortisol.