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Cortisol responses to the insulin hypoglycaemia test in children
P M Crofton1, A C Don-Wauchope, L E Bath
1Department of Paediatric Biochemistry, Royal Hospital for Sick Children, Edinburgh, UK. patricia.crofton@luht.scot.nhs.uk
Aim:
To determine the timing of the peak cortisol response to the insulin hypoglycaemia (IH) test in children and to establish paediatric reference data.
Methods:
We retrospectively reviewed all IH tests in a tertiary paediatric endocrine referral centre over a 6-year period. Inclusion criteria were age <16 years and adequate hypoglycaemia (glucose < or =2.0 mmol/l). Patients with an impaired hypothalamic-pituitary-adrenal axis or receiving glucocorticoid medication were excluded. Fifty-four subjects (35 males) met the criteria. Blood samples were collected at -30, 0, 20, 30, 60, 90, 120, and 150 min in relation to insulin bolus injection (0.15 U/kg) at 0 min. Glucose, cortisol, and growth hormone (GH) were measured in all samples.
Results:
Peak cortisol and GH responses occurred by 90 min in all subjects. Peak cortisol was inversely correlated with age (rs -0.65, p<0.0001). The median (5th centile) peak cortisol value was 689 nmol/l (547 nmol/l) in children younger than 10 years as compared with 555 nmol/l (468 nmol/l) in those older than 10 years (p<0.0001). Peak cortisol was not related to peak GH (rs -0.20, p=0.15).
Conclusions:
Blood sampling in the IH test may be curtailed 90 min after injection. The peak cortisol response to IH is age related.