The relationship between 63 days of 24-h urinary free cortisol and hair cortisol levels in 10 healthy individuals

Background: Interest in measuring cortisol in scalp hair is increasing because of its assumed ability to provide a historical timeline of previous systemic levels of cortisol. Yet, it remains uncertain how well hair cortisol represents the total systemic secretion of cortisol over time. Methods: Ten healthy individuals collected 24-h urine samples for 63 consecutive days and provided a hair sample at the end of the study period. 24-h urinary creatinine levels in every urine sample were determined to assess completeness of the samples. Cortisol levels in 24-h urine samples and in hair were measured with liquid chromatography tandem mass spectrometry. The correlations between urinary cortisol and hair cortisol were calculated using Kendall's tau. Results: We found a nonsignificant moderate correlation between average urinary cortisol secretion and average hair cortisol concentration r(t) = 0.422, p = 0.089. Conclusions: Hair cortisol concentration correlates low to moderately with 24-h urinary cortisol concentration over a period of 63 days. (C) 2016 Elsevier Ltd. All rights reserved.