Do you use absolute random cortisol levels or delta cortisol levels after ACTH stimulation to diagnose adrenal insufficiency in the critically ill?  

As reviewed recently by Dr. Teblick et al., PMID 35358303, this is still a controversial and complex issue. Based on many studies, it would be preferable to avoid ACTH stimulation unless there is rapid availability of free cortisol. Random total cortisol is probably the better alternative.

Only random cortisol levels.