This thesis can be subdivided in two parts.

The first part focuses on validating a novel method for measuring long-term cortisol concentrations in scalp hair, which has been developed in adults, for use in pediatric clinical practice and research. Additionally, we focused on improving this method by developing a LC-MS/MS based method for scalp hair measurement and validating this method in children as well.

In the second part of this thesis, both the immune-assay based and LC-MS/ MS based methods are applied to challenges in clinical research and practice. The associations between glucocorticoids and metabolic adversities appear convincing in the case of Cushing’s disease, but remain to be proven in more subtle forms of hypercortisolism. Recent studies provide strong support for a positive association between long-term cortisol measured in scalp hair and cardiovascular disease and the metabolic syndrome in adults. We assessed the relation between long-term cortisol and obesity in children. Additionally, we evaluated measurement of long-term cortisol concentrations and adrenal precursor hormones as a monitoring tool in the followup of hydrocortisone treatment in children with adrenal insufficiency and congenital adrenal hyperplasia.