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Urinary 6 beta-hydroxycortisol in humans: analysis, biological variations, and reference ranges
1Department of Medical Technology, School of Allied Health Sciences, University of Texas Medical Branch, Galveston 77555-1028, USA.
Objective:
To evaluate methods for analysis, biological variation, and reference ranges for 6 beta-hydroxycortisol in urine.
Methods:
The urinary level of 6 beta-hydroxycortisol (6 beta-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 6 beta-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 6 beta-OHF and urinary free cortisol (UFC) were quite parallel to each other, so that the ratio of 6 beta-OHF to UFC remained constant through the day.
Conclusion:
An early morning urine specimen can provide the urinary ratio of 6 beta-OHF to UFC as adequately as that determined from 24-h specimen.