Introduction The insulin tolerance (ITT) and glucagon stimulation (GST) tests are used most frequently to assess growth hormone reserve. These tests also stimulate cortisol release. It is not uncommon for patients, with no clinical suggestion of cortisol deficiency, to have equivocal cortisol responses (peak cortisol <500 nmol/L) which may cause unnecessary parental anxiety, further testing and treatment.

Aim To explore the outcome of children with idiopathic short stature and isolated idiopathic short stature who had peak cortisol levels <500 nmol/l in the ITT or GST during the period January 2008 to December 2014.

Results Data from 189 (130 M) patients, age 12.0 years ± 4.4 (mean±SD) were studied. 94 underwent a GST and 95 underwent an ITT.

In 38 patients (20.1%), age 12.1yrs (1.7–19.2 yrs), peak cortisol levels were <500 nmol/L, of whom 24 patients, (median age 7.7 yrs, 1.7–16.8 yrs) underwent GST (peak cortisol levels 396 nmol/L, 231–491) and 14 patients (median age 14.0 yrs, 5. 2–19.2 yrs) underwent ITT (peak cortisol 461 nmol/L, 408–497).

Outcome of these patients who had peak cortisol <500 nmol/l is given in the following Table.

Conclusion Our observations support previous reports that cortisol levels in healthy children may be <500nmol/L on the GST and ITT, and strengthen recommendations for a review in the definitions of ‘normal’ and ‘abnormal’ results.