Re-Evaluation of the Diagnostic Cut-Off for the Overnight Metyrapone Test Using Liquid Chromatography–Tandem Mass Spectrometry Measurement of 11-Deoxycortisol

The overnight metyrapone test is an established tool for assessing the hypothalamic-pituitary-adrenal axis. The current diagnostic cut-off for serum 11-deoxycortisol (70 µg/L) is based on older immunoassays. With the introduction of liquid chromatography-tandem mass spectrometry, concerns have arisen regarding the validity of these thresholds. This study re-evaluates 11-deoxycortisol measured by liquid chromatography-tandem mass spectrometry in the overnight metyrapone test and assesses whether current cut-offs remain appropriate. In this retrospective diagnostic study, patients undergoing single-dose metyrapone testing after pituitary surgery (2017-2025) were included. Serum 11-deoxycortisol was measured using liquid chromatography-tandem mass spectrometry. A sufficient adrenal function was classified based on the absence of glucocorticoid therapy, lack of symptoms, normotension and normal laboratory findings. Receiver operating characteristic analysis was used to determine optimal thresholds. Diagnostic performance was evaluated using sensitivity, specificity, likelihood ratios, Matthews correlation coefficient, and bootstrap validation. Receiver operating characteristic analysis showed strong discrimination for detecting secondary adrenal insufficiency (area under the curve=0.953). Multiple statistical approaches consistently identified optimal cut-offs below 70 µg/L, in line with recent studies. Thresholds around 63-64 µg/L improved the balance between sensitivity and specificity. In contrast, the historical cut-off of 70 µg/L showed high sensitivity but reduced specificity, increasing the risk of false-positive results and unnecessary glucocorticoid substitution. The currently recommended cut-off for the OMT may be too high when using liquid chromatography-tandem mass spectrometry. Lower thresholds around 63-64 µg/L may improve diagnostic accuracy. Re-evaluation of current recommendations appears warranted.