Objective: The aim of glucocorticoid replacement therapy in ACTH-deficient patients is to mimic the normal diurnal variation of cortisol. However, current hydrocortisone (HC) replacement results in prolonged episodes of hypocortisolaemia and supraphysiological peaks. Plasma cortisol profiles are an accurate yet labour-intensive method of assessing HC replacement. Salivary and bloodspot cortisol sampling methods are less invasive and may be useful tools for assessing glucocorticoid replacement, particularly in children. Therefore, we aimed to define normal salivary and bloodspot cortisol levels in children and their correlations with the gold standard (plasma cortisol).
Design: Cross-sectional study in a paediatric teaching hospital.
Methods: Plasma, saliva and bloodspot cortisol profiles were performed on 30 ACTH-deficient children and 22 healthy siblings.
Results: In ACTH-deficient patients taking oral HC, the bloodspot–plasma correlation (ρ = 0.90) was stronger than the salivary–plasma correlation (ρ = 0.49). Using target ranges for salivary and bloodspot cortisol levels based on normal data from control subjects, the less invasive sampling methods had low rates of agreement with plasma cortisol target ranges (saliva 65% and bloodspot 75%). Using the plasma–bloodspot correlation regression equation to convert bloodspot to calculated plasma cortisol, there was a high concordance between calculated and actual measured plasma cortisol (88%).
Conclusion: Bloodspot cortisol sampling is a feasible and accurate method for monitoring oral HC replacement in paediatric patients without necessitating hospital admission, but salivary sampling is not useful.