Development and internal validation of a predictive score for the diagnosis of central adrenal insufficiency when morning cortisol is in the grey zone

BACKGROUND: When evaluating a patient for central adrenal insufficiency (CAI), there is a wide range of morning cortisol values for which no definite conclusion on hypothalamus–pituitary–adrenal (HPA) axis function can be drawn; in these cases, a stimulation test is required. Aim of this study was to develop an integrated model for CAI prediction when morning cortisol is in the grey zone, here defined as 40.0–160.0 μg/L. METHODS: Overall, 119 patients with history of sellar tumour which underwent insulin tolerance test (ITT) for the evaluation of HPA axis were enrolled. Supervised regression techniques were used for model development. RESULTS: An integrated predictive model was developed and internally validated, and showed a significantly better diagnostic performance than morning cortisol alone (AUC 0.811 vs 0.699, p = 0.003). A novel predictive score (CAI-score) was retrieved, on a 5.5-point scale, by considering morning cortisol (0 points if 130.1–160.0 μg/L, 1 point if 100.1–130.0 μg/L, 1.5 points if 70.1–100.0 μg/L, 2.5 points if 40.0–70.0 μg/L), other pituitary deficits (2 points if ≥ 3 deficits), and sex (1 point if male). A diagnostic algorithm integrating CAI-score and ITT was finally proposed, with an overall accuracy of 99%, and the possibility to avoid the execution of stimulation tests in 25% of patients. CONCLUSIONS: This was the first study that proposed an integrated score for the prediction of CAI when morning cortisol is in the grey zone. This score might be helpful to reduce the number of patients who need a stimulation test for the assessment of HPA axis function. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s40618-022-01926-z.