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 rт = 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.

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