Diurnal excretion of urinary cortisol, cortisone, and cortisol metabolites in chronic fatigue syndrome

ObjectiveThe aim of this study was to obtain comprehensive information on basal hypothalamic–pituitary–adrenal (HPA) axis activity in chronic fatigue syndrome (CFS) patients who were not affected by medication or comorbid psychiatric disorder likely to influence the HPA axis.MethodSteroid analysis of urine collections from 0600 to 2100 h at 3-h intervals in CFS patients and in controls.ResultsUrinary free cortisol and cortisone concentrations showed a significant normal diurnal rhythm, but levels were lower across the cycle in CFS. In contrast, while urinary cortisol metabolites also showed a normal diurnal rhythm, levels were not significantly different between the CFS and controls at any time. Derived metabolite ratios were similar in both groups.ConclusionThis study provides further evidence for reduced basal HPA axis function in patients with CFS, based on lower free cortisol and cortisone levels, but this is not corroborated by cortisol metabolite data. The difference between these measures cannot be explained by an altered timing of the diurnal rhythm.