Validity and reliability of method used to analyse hair cortisol concentration

Hair cortisol analysis is a method of analysing the stress hormone cortisol that offers great potential for helping researchers understand the long-term impact of stress and distress on the body. Hair analysis not only provides an excellent method of studying the average production of cortisol over weeks and months, but also the potential to understand cortisol levels several months before the hair was collected. Whilst research with hair samples for cortisol analysis is a fast-developing field, there has been less analysis of the methods used to analyse hair cortisol. We report two studies where the novel hair analysis method developed at the Anglia Ruskin university (ARU) Biomarker Laboratory was tested for reliability and validity. In study 1, 32 participants provided hair samples for an examination of the reproducibility of the hair cortisol analysis method. In study 2, 53 participants provided a hair sample cut from the scalp, and the methanol that the cortisol was extracted into was split between two tubes and assayed at two different laboratories with different methods (ELISA, LC-MS/MS). Overall, the results demonstrate that the methods developed to analyse hair cortisol in the ARU Biomarker Laboratory were both reliable and valid. The discussion considers further avenues for research and optimisation of the methodology.