Urinary 6β-Hydroxycortisol in Humans: Analysis, Biological Variations, and Reference Ranges

Methods: The urinary level of 6β-hydroxycortisol (6β-OHF) was measured by reversed-phase high performance liquid chromatography. Results: The method was accurate and precise, as indicated by a recovery rate of 92-95% and less than 5.5% and 6.6% of coefficient of variation for within-run and between-run assay, respectively. The reference range of urinary 6β-OHF was 187-1245 nmol/day in adults (20-60 years) and 103-915 nmol/day in the elderly (>61 years). No significant day-to-day intrabiological variation was observed in a 5-day period. Diurnal rhythms of urinary 6β-OHF and urinary free cortisol (UFC) were quite parallel to each other, so that the ratio of 6β-OHF to UFC remained constant through the day. Conclusion: An early morning urine specimen can provide the urinary ratio of 6β-OHF to UFC as adequately as that determined from 24-h specimen.