Diagnosing adrenal insufficiency using ACTH stimulation test

To the Editor:

We read with interest the real-world data of Nanzer et al. [1], looking at adrenal insufficiency (AI) in severe asthma patients taking oral corticosteroid-sparing anti-interleukin (IL)-5 therapy. They reported that 43% of patients apparently failed a short adrenocorticotropic hormone (ACTH) stimulation test associated with a median baseline morning serum cortisol of 86 nmol·L⁻¹ and a median prednisolone dose of 5 mg. We would be interested to know the mean cortisol level after ACTH, as well as the percentage of patients who failed to achieve a post-ACTH level of 500 nmol·L⁻¹ which is the accepted cut-off for impaired response [2, 3]. Pointedly they used a pharmacological 250 µg dose of ACTH instead of the more physiological 0.5–1 µg dose [3, 4]. We suggest that using the correct ACTH dose in conjunction with a 500 nmol·L⁻¹ cortisol cut off would be accompanied by a higher proportion of patients designated with AI. Finally, we also note that their patients were taking high-dose inhaled corticosteroid at a fluticasone propionate equivalent dose of 1 mg·day⁻¹. In this regard, 1 mg of inhaled fluticasone propionate exhibits a cortisol suppressive potency equivalent to 8.5 mg of oral prednisolone [5]. Hence, while it might have been possible to wean the prednisolone dose to 5 mg on anti-IL-5, in reality patients were likely to have been exposed to a much higher total systemic corticosteroid burden.

Shareable PDF