Correlation analysis of cortisol concentration in hair versus concentrations in serum, saliva, and urine

Cortisol concentration is measured in blood, urine, and saliva samples. It has been recently proven that cortisol could also be detected in hair samples. Cortisol measurements in different samples have their own individual characteristics and clinical utility. We aimed to investigate the correlation between hair cortisol concentration and standard cortisol measurements used in clinical practice.

Fifty adult volunteers with a negative history of endocrine disorders were enrolled in the study. Morning serum cortisol (MSC), evening serum cortisol (ESC), evening free salivary cortisol (EFSC), urine free cortisol (UFC), and hair cortisol concentration (HCC) were analysed in all participants. Eventually, 41 volunteers were included into the study, whose cortisol concentration in the 1 mg overnight dexamethasone suppression test (1 mg ONDST) were < 50 nmol/L, and cortisol levels in serum, saliva, and urine were within reference ranges. Hair cortisol concentration test was performed for 20 mg of hair strands of the proximal 1 cm hair segments.

Hair cortisol concentration ranged from 0.3036 to 2.65 nmol/mg, and the average value was 0.8125 ± 0.4834 nmol/mg. No significant correlations were found between HCC and MSC (rho = 0.04419, p = 0.7838), HCC and ESC (rho = -0.2071, p = 0.1938), HCC and EFSC (rho = 0.1005, p = 0.532), or HCC and UFC (rho = 0.1793, p = 0.262).

This work is another step in the discussion on the application of HCC determinations in clinical practice. Our results have showed no correlations between HCC and single point cortisol assessment in blood, saliva, and urine in patients with reference cortisol levels.