Objective
To examine serum cortisol responses to a simplified low dose short Synacthen test (LDSST) in children treated with inhaled corticosteroids (ICS) for asthma and to compare these to early morning salivary cortisol (EMSC) and cortisone (EMSCn) levels.

Design
EMSC and EMSCn samples were collected for three consecutive days. On day three Synacthen 500ng/1.73m2 was administered intravenously. Samples were collected at 0, 15, 25, 35 minutes.

Results
269 subjects (160 M: 109F), median (range) age 10.0 (5.1 – 15.2) years were studied. Peak cortisol in the LDSST was <500nmol/L in 101 subjects (37.5%) and <350nmol/L in 12 subjects (4.5%). Basal cortisol correlated with peak cortisol: r=0.55, (95% CI: 0.46, 0.63, p<0.0001). Time at which peak cortisol concentration was achieved was significantly related to the value of peak cortisol (p<0.0001), with higher cortisol peaks occurring later in the test and lower cortisol peaks occurring earlier. EMSC and EMSCn had no predictive value for the identification of patients with a peak cortisol <500nmol/L. EMSCn was superior to EMSC in identifying patients with a peak cortisol < 350nmol/L: a minimum EMSCn cut-off value of 12.5 nmol/L gave a negative predictive value of 99.2% and positive predictive value of 30.1%.

Conclusion
Our data illustrate that basal measures of cortisol are likely to be of value in screening populations for patients at greatest risk of adrenal crisis. EMSCn shows promise as a screening tool for the identification of patients with severe adrenal insufficiency.