Objective The circadian hormone melatonin has wide-reaching effects on human physiology. In adolescents, the impact of nighttime light exposure and other modifiable behavioral factors on melatonin levels is poorly understood. Design We cross-sectionally examined the influence of nighttime behaviors on melatonin levels in 100 adolescents (average age: 15.7; 55 female, 45 male), who completed a self-administered questionnaire and provided a first morning urine sample to assay for urinary 6-sulfatoxymelatonin (aMT6s) levels. We used mixed-effects regression models to test for differences in aMT6s levels by categories of covariates. Results Self-reported sleep duration, ambient light levels during sleep, and use of electronics after turning off lights did not significantly predict aMT6s levels. Compared to those who reported weekend bedtimes before 11pm, urinary aMT6s levels were significantly lower among participants reporting weekend bedtimes after midnight (52.5 vs. 38.0 ng/mg creatinine, Ptrend=0.007). Sleep interruption also appeared to be significantly associated with lower urinary aMT6s levels, but only if lights were turned on during sleep interruption (43.0 ng/mg creatinine for participants with sleep interruption but not turning lights on, vs. 24.6 ng/mg creatinine for participants reporting that they turned on the light when their sleep was interrupted Pdifference=0.032). Conclusions Our study suggests that self-reported sleep-related behaviors have little to no effect on adolescent circadian systems, though larger studies are needed to confirm our findings.

Blood cortisol level is routinely analysed in laboratory medicine, but the immunoassays in widespread use have the disadvantage of cross-reactivity with some commonly used steroid drugs. Mass spectrometry has become a method of increasing importance for cortisol estimation. However, current methods do not offer the option of accurate mass identification. Our objective was to develop a mass spectrometry method to analyse salivary, serum total, and serum free cortisol via accurate mass identification. The analysis was performed on a Bruker micrOTOF high-resolution mass spectrometer. Sample preparation involved protein precipitation, serum ultrafiltration, and solid-phase extraction. Limit of quantification was 12.5 nmol L(-1) for total cortisol, 440 pmol L(-1) for serum ultrafiltrate, and 600 pmol L(-1) for saliva. Average intra-assay variation was 4.7%, and inter-assay variation was 6.6%. Mass accuracy was <2.5 ppm. Serum total cortisol levels were in the range 35.6-1088 nmol L(-1), and serum free cortisol levels were in the range 0.5-12.4 nmol L(-1). Salivary cortisol levels were in the range 0.7-10.4 nmol L(-1). Mass accuracy was equal to or below 2.5 ppm, resulting in a mass error less than 1 mDa and thus providing high specificity. We did not observe any interference with routinely used steroidal drugs. The method is capable of specific cortisol quantification in different matrices on the basis of accurate mass identification.

Objective: The role of cortisol in the prediction of mortality risk in critical illness is controversial in the literature. The aim of this study was to evaluate the prognostic value of cortisol concentrations in a mixed population of critically ill patients in medical emergencies. Design: In this prospective, observational study, measurement of total (TC) and free cortisol (FC) levels was made in the serum samples of 69 critically ill patients (39 males and 30 females, median age of 74 years) at admission (0 h) and 6, 24, 48, and 96 h after admission. Methods: Cortisol levels were determined using HPLC coupled high-resolution ESI-TOF mass spectrometry. The severity of disease was calculated by prognostic scores. Statistical analyses were performed using the SPSS 22.0 software. Results: The range of TC varied between 49.9 and 8797.8 nmol/l, FC between 0.4 and 759.9 nmol/l. The levels of FC at 0, 6, 24, and 48 h and TC at 0, 6 h were significantly elevated in non-survivors and correlated with the predicted mortality. The prognostic value of these cortisol levels was comparable with the routinely used mortality scores. In predictive models, FC at 6, 24, and 48 h proved to be an independent determinant of mortality. Conclusions:The predictive values of FC in the first 2 days after admission and TC within 6 h are comparable with the complex, routinely used mortality scores in evaluating the prognosis of critically ill patients. The cortisol response probably reflects the severity of disease.

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