Purpose: Recently, hair cortisol has become a topic of global interest as a biomarker of chronic stress. Different research groups have been using different methods for extraction and analysis, making it difficult to compare results across studies. A critical examination of the reported analytical methods is important to facilitate standardization and allow for a uniform interpretation.
Methods: This study qualitatively compared four published procedures from laboratories in Germany, the Netherlands, USA and Canada. Multiple aspects of their procedures were compared.
Results: A major difference among the laboratories was the ELISA kit used: the Canadian laboratory used the kit from ALPCO Diagnostics (Salem, MA, USA), the American laboratory used the kit from DRG International (Springfield, NJ, USA), the German laboratory used the kit from DRG Instruments GmbH (Marburg, Germany), or IBL (Hamburg, Germany), and the Dutch used the kit from Salimetrics (Suffolk, UK). In addition, there are noted differences in hair mass used as well as washing and extraction procedures. The range of hair cortisol levels determined in healthy volunteers by the four groups was within 2.3-fold: Koren, 46.1 pg/mg; Van Rossum, 29.72 pg/mg; Kirschbaum, 20 pg/mg and Laudenslager ~ 27 pg/mg.
Conclusions: The relative similarities in hair cortisol values in volunteers among the four laboratories should facilitate a quality assurance exchange program, as a necessary step toward clinical use of this novel test.