S34 The role of baseline morning cortisol as a guide to assess adrenal failure in severe steroid dependent asthma

Introduction With the successful introduction of biologic agents for severe eosinophilic asthma (SEA), prednisolone-dependent patients are increasingly able to wean their maintenance steroids. We have previously reported on the prevalence of adrenal insufficiency (AI) in this patient cohort.1 Strategies for how and when to test adrenal reserve vary. The morning cortisol is a simple, cheap (£2.79) test and can be done locally; the short-synacthen-test (SST) is expensive (£38), invasive, time-consuming and not risk free but it is often considered mandatory for the reliable assessment of adrenal reserve. We present our experience of considering hypothalamo-pituitary-adrenal (HPA)-axis testing and the use, and misuse of the SST. Methods We conducted a retrospective review of 120 consecutive patients with SEA who started on biologic therapy between May 2017–2018. Steroid-dependent patients able to reduce their prednisolone to ≤7.5 mg/day and who had an HPA-axis assessment with a morning cortisol and/or SST were included in the analysis. Cortisol was assayed on a Roche-II, with 7.9% cross reactivity to prednisolone. Results 72/120 patients (60%) were on maintenance prednisolone, 35/72 (49%) of these had an SST in addition to a morning cortisol. 15/35 (43%) patients failed the SST; they had a median 9am cortisol of 82nmol/l (CI: 41–120) and were taking a median daily dose of 5 mg prednisolone. Patients who passed the SST (20/35 (57%)) had a median 9am cortisol of 220 nmol/l (CI: 189–250) and were on average taking 3 mg prednisolone daily at the time of testing. 100% of patients with a morning cortisol of 250nmol/l passed the SST (figure 1). Adopting these cut-offs would have prevented 12 (34%) SST. Conclusion In this cohort of steroid dependent asthma patients, a morning cortisol of 250nmol/L was predictive in identifying patients with or without AI. We propose measurements of the serum morning cortisol level once the patient is on ≤5 mg prednisolone daily has utility in guiding the clinician as to which patient may need dynamic assessment of adrenal reserve and in whom it should not be done. Reference Raheem, et al. Thorax 2018;73(Suppl 4):A174