Determination of cortisol cut-off limits and steroid dynamics in ACTH stimulation (Synacthen®) test: A comparative analysis using Roche Elecsys Cortisol II immunoassay and LC-MS/MS

Abstract

Purpose Measurement of cortisol concentrations is method dependent. Therefore, assay-specific cut-off limits for the definition of e.g., adrenal insufficiency should be available. The study aimed to establish assay-specific cut-off limits for cortisol after adrenocorticotropic hormone (ACTH) stimulation, comparing Roche Elecsys Cortisol II immunoassay to liquid chromatography-mass spectrometry (LC-MS/MS). Methods One hundred healthy participants underwent a ACTH test (250 µg), with plasma samples analyzed using ElecsysCort I, ElecsysCort II, and LC-MS/MS. Cortisone, corticosterone, 17-OH-progesterone, dehydroepiandrosterone sulfate (DHEAS), androstenedione, and testosterone were additionally analyzed with LC-MS/MS. Reference intervals were defined as the 2.5-97.5th percentiles, while the cut-off limit for a normal cortisol response to the ACTH test was defined as: 2.5th percentile − 1.96×SE. Results ElecsysCort II measured cortisol concentrations 21% (95% CI: 19–22%) lower than ElecsysCort I. Cut-off limits for cortisol 30 and 60 minutes after ACTH were 426 and 485 nmol/L (ElecsysCort II) and 411 and 470 nmol/L (LC-MS/MS). The ACTH test resulted in significantly higher plasma corticosterone, androstenedione, dehydroepiandrosterone sulfate (DHEAS), and 17-OH-progesterone concentrations but decreased cortisone concentrations in both sexes. Testosterone decreased significantly in men (1.9 nmol/L, 95% CI: 1.3–2.5) but increased in women. Conclusion ElecsysCort II has high analytical performance and yields significantly lower cortisol concentrations than prior polyclonal immunoassays. This clinically relevant difference underscores the necessity to revise cut-offs for improved diagnostic precision. Recommended 30-minute cortisol cutoff limits are 411 nmol/L (LC-MS/MS) and 426 nmol/L (ElecsysCort II). Adrenocortical steroids increased upon ACTH stimulation, except for cortisone in both sexes and testosterone in men, both of which decreased.