Spot and morning cortisol in comparison to low dose short Synacthen® test

Abstract

Objective. While the low dose short Synacthen® test (LDSST) is considered to be the gold standard to evaluate adrenal function, it is labor-intensive, invasive and inconvenient. The aim of the study is to identify cut-offs for spot serum cortisol for in-patients and morning serum cortisol for out-patients. The study also aims to describe the disease spectrum leading to suspicion of adrenal insufficiency in a Chinese out-patient cohort. Methodology. Adult patients were recruited from a tertiary hospital in Hong Kong. 423 in-patients were included consecutively from July 2013 to December 2013, and 422 out-patients from June 2014 to October 2014. Serum cortisol responses at 0, 20 and 30 minutes were evaluated. Results. For in-patients admitted for acute illness, a spot serum cortisol of ≤92 nmol/L indicated adrenal insufficiency, and a value of ≥494 nmol/L signaled adequate adrenal reserve. The respective morning cortisol values for out-patients who were ambulatory and not under stress were ≤124 nmol/L and ≥428 nmol/L. The percentage of unnecessary LDSST was higher in the in-patient cohort than the out-patient cohort (43% and 37%, respectively). The most common referral for out-patient LDSST was for suspected iatrogenic Cushing’s syndrome (ie: iatrogenic adrenal suppression) from Rheumatology. Conclusions. The LDSST is of little added value in in-patients with spot serum cortisol of ≤92 nmol/L or ≥494 nmol/L and out-patients with morning serum cortisol of ≤124 nmol/L or ≥428 nmol/L. Spot and morning cortisol levels, for in and out-patients respectively, should be incorporated into endocrine protocols preceding the LDSST in the workup of adrenal insufficiency.