Toward standardization of hair cortisol measurement: results of the first international interlaboratory round robin.
BACKGROUND
The importance of hair cortisol as a long-term retrospective measure of systemic cortisol exposure is being increasingly recognized, and over recent years, the field of hair cortisol analysis has seen rapid expansion with laboratories around the globe, integrating hair cortisol analysis into their study designs. These laboratories use different methods of analysis, and presently, no attempt has been made to compare them. To move toward clinical utilization of this novel method, international benchmark reference values must be established. For that end, 4 leading laboratories in hair cortisol testing set up a protocol for comparison of the methods used by them.


METHODS
Four immunoassay methods and 2 liquid chromatograph-mass spectrometry (LC-MS/MS) methods were compared by analyzing the same hair samples representing the low, intermediate, and high ranges of hair cortisol concentrations (HCC).


RESULTS
HCC determined by the 4 immunoassay methods were highly and positively intercorrelated (r(2) between 0.92 and 0.97; all P < 0.0001) in all comparisons of individual laboratories. Additionally, each laboratory's immunoassay HCC had significant positive correlations (r(2) between 0.88 and 0.97; all P < 0.0001) with each of the 2 LC-MS/MS methods, which produced practically identical results.


CONCLUSIONS
This study indicates that laboratories using immunoassays can use a correction factor that will convert results into standard LC-MS/MS equivalents.
*Western University, London, Ontario, Canada; †Dresden University of Technology, Germany; ‡Anschutz Medical Campus, University of Colorado, Denver; §Department of Internal Medicine, Erasmus MC, University Medical Center Rotterdam, the Netherlands; and ¶University of Toronto, Ontario, Canada.
Evan
E
Russell
Clemens
C
Kirschbaum
Mark L
ML
Laudenslager
Tobias
T
Stalder
Yolanda
Y
de Rijke
Elisabeth F C
EF
van Rossum
Stan
S
Van Uum
Gideon
G
Koren
D019985:Benchmarking; D002851:Chromatography, High Pressure Liquid; D003429:Cross Reactions; D004797:Enzyme-Linked Immunosorbent Assay; D006197:Hair / Q000737:chemistry*; D006801:Humans; D006854:Hydrocortisone / Q000032:analysis*; D007118:Immunoassay; D012015:Reference Standards; D012016:Reference Values; D015203:Reproducibility of Results; D053719:Tandem Mass Spectrometry
D006854:Hydrocortisone