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