Circadian rhythm of urinary steroid metabolites

Background Samples submitted for urinary steroid profile analysis are often untimed, but influence of collection time on interpretation is unknown. We report circadian rhythms of the major steroid metabolites and derived ratios in urine collected at 3-h intervals over 24 h, after first establishing that disturbance of sleep associated with collection does not alter rhythms on the succeeding day. Methods Assay of steroid metabolites (gas chromatography) and creatinine in urine collections made by 10 men and 10 women every 3 h starting at 2100 for 24 h. Data were subjected to cosinor analysis. Results Summed cortisol and androgen metabolites exhibited significant circadian rhythms, as expected, but with a surprisingly long time-lag (maxima at around 1400). Amplitudes were different, so that the ratio cortisol/androgen metabolites also showed a significant rhythm. The ratios 5 alpha/5 beta tetrahydrocortisol and 20-hydroxy/20-oxo cortisol metabolites showed significant rhythms which were not in phase with total cortisol metabolites, while 11-hydroxy/11-oxo cortisol metabolites showed no rhythm. There were no gender differences in time of maxima. Previously established gender differences in metabolite levels were confirmed. Creatinine levels showed no circadian rhythm. Conclusion Circadian variation should be considered when interpreting results from urine steroid analysis. Calculation of steroid/steroid or steroid/creatinine ratios is not informative in untimed collections.