Endocrine Abstracts

Introduction: Diagnostic cut-offs for plasma cortisol on Short Synacthen Test (SST) are controversial, made more complicated by modern assays and paediatric normative values extrapolated from adult data. Some advocate a division between biochemical and clinical AI, with different cut-offs and management strategies. For asymptomatic children, with a low-index of suspicion, and borderline SST results our department has evolved a tendency to advise hydrocortisone replacement in times of stress only. We analysed three years of SST data, examining the cases with borderline peak cortisol results for aetiological links and subsequent management strategies.

Methods: Retrospective analysis of all SST performed between September 2014 and 2017 was undertaken. Plasma cortisol samples were analysed on the Abbott Architect i1000 immunoassay (CVs <5%). Our diagnostic threshold for a ‘pass’ for both high (HDT) and low-dose SST (LDT) is 450 nmol/l. ‘Borderline’ peak cortisol was considered to be 300–449 nmol/l and this group was further subdivided into 300–349, 350–399 and 400–449 nmol/l for analysis in terms of demographics, test indication, dose of synacthen and resultant management plan.

Results: 433 SSTs were performed, 74 (41M) of whom had a borderline peak cortisol (16.7%). The proportion of borderline tests remained similar each year, despite an increasing trend towards HDT over LDT. Management of patients with borderline peak cortisol varied, however there was a tendency to reduce or stop replacement glucocorticoids with higher results, particularly after a HDT. Steroids were more likely to be started or continued with lower borderline values. Patients with known AI were more likely to have their steroids continued or SST repeated at lower peak cortisols and weaned at higher peak cortisols. Those without established AI were less likely to have glucocorticoid replacement commenced if higher borderline value, particularly following a LDT.

Conclusions: There was significant variation in the management of borderline SST results with the same cortisol result warranting commencement of regular replacement for one physician and stopping replacement for another. There is a paucity of research in this area and studies to examine both the natural course of children with borderline SSTs and whether stress cover represents pragmatic but safe management are warranted.