Another common finding is corticosteroid insufficiency related to critical illness, a condition associated with increased mortality. The diagnosis of this condition is challenging, as the usefulness of the ACTH test as well as the type of cortisol assay that should be used are still debated. Molenaar et al. [22] compared the values of total and free cortisol after an ACTH test. They found in a set of 112 patients (49 with sepsis) that the diagnosis of adrenal failure was not affected by the type of test used, as free and total cortisol measurements were closely related. These findings could have important implications for daily practice.