Endocrine Abstracts

Background: Short Synacthen Tests (SSTs) are integral to the diagnosis of Adrenal Insufficiency (AI). A 30-minute stimulated cortisol value is assessed against local assay dependent thresholds to ascertain or exclude the diagnosis. A diagnosis of AI is a life changing event requiring the initiation of life long glucocorticoid replacement therapy for survival. Glucocorticoid replacement is associated with long term morbidity and mortality, including an increased risk of diabetes, cardiovascular disease and osteoporosis. It is essential therefore that the diagnosis of AI is secure, and a lifetime of replacement not commenced inappropriately.

Methods: SSTs performed at North West London Pathology were isolated from 60,178 cortisol tests performed between May 2016 and February 2020. Patient electronic medical records were exhaustively reviewed longitudinally to assess whether a diagnosis of AI was correctly or incorrectly applied, based on expert assessment.

Results: SST data was isolated for 670 patients. Receiver Operator Curve analysis identified that an SST cut-off of 370 nmol/l at 30 minutes achieved a sensitivity and specificity of 97.4% and 93.4% respectively. A 60-minute cut-off of 420 nmol/l produced a 97.4% sensitivity and 93.1% specificity. A total of 628 patients passed their SSTs: 140 (22.3%) patients passed at 60 minutes but would have failed at 30 minutes, according to biochemical criteria. Only 2 of these patients were later prescribed glucocorticoids. In one patient, there was unrelated pituitary tumour regrowth, and the other later discontinued their replacement therapy.

Conclusions: SST thresholds for Abbott cortisol assays can be lowered to to 420 nmol/l at 60 minutes and 370 nmol/l at 30 minutes, and both timepoints should be routinely performed. The above recommendations should reduce the number of patients who are inappropriately labelled with a diagnosis of AI, thereby avoiding the associated deleterious effects of inappropriate glucocorticoid replacement therapy.