Validation and Reference Ranges of Hair Cortisol Measurement in Healthy Children

<b><i>Background:</i></b> Cortisol is produced in a circadian rhythm controlled by the hypothalamus-pituitary-adrenal axis, making it cumbersome to measure long-term cortisol exposure. Hair has proven to be a reliable matrix for long-term cortisol measurement in adults and can be used as diagnostic tool for (cyclic) Cushing's syndrome. The diagnostic applicability in children has not been studied, nor have the effects of development and hair care been evaluated in children. We aimed to establish reference ranges of hair cortisol concentrations (HCC) in healthy children and to evaluate the effects of age, gender, puberty and characteristics of hair care. <b><i>Methods:</i></b> In 128 healthy children aged 4-14 years, HCC were measured in a small 3-cm hair lock from the back of the head. <b><i>Results:</i></b> HCC increased with age (p = 0.04) up to age 10 years, with a mean of 5.0, 5.8, 6.8 and 8.5 pg/mg at age 4-5, 6-7, 8-9 and 10-14 years, respectively. Children aged 4-7 years had significantly lower HCC compared to healthy adults (p = 0.007). We did not find any influence of gender, puberty or hair care characteristics on hair cortisol. <b><i>Conclusion:</i></b> HCC can be reliably measured in childhood, and reference ranges increase with age. HCC in children are not dependent on hair care or hair characteristics.