title: [Fooled by the diurnal rhythm].
abstract: BACKGROUND
  Under ordinary circumstances, the daily secretion of cortisol displays a characteristic diurnal variation with a peak in the morning and a trough at night. It is important to understand the variation in cortisol secretion when analysing results of cortisol tests.
  
  
  METHODS
  We present a patient in whom work-up for acute headache revealed a pathologically low morning serum cortisol level. This led to further evaluation of adrenocortical function with an adrenocorticotropic hormone (ACTH) stimulation test and cortisol day profiles in serum and saliva.
  
  
  CONCLUSIONS
  The analyses showed normal adrenocortical function and diurnal variation with normal amplitudes. The morning rise in cortisol secretion was, however, delayed by 7-8 hours due to a delayed sleep phase. This case illustrates the importance of the diurnal rhythm in the assessment of pituitary-adrenal function. There should be clinical suspicion of a disorder before a test is requested.
authors.affiliation: Medisinsk avdeling, Haukeland Universitetssykehus, Bergen. kristian.lovas@helse-bergen.no
authors.forename: Kristian
authors.initials: K
authors.lastname: Løvås
authors.forename: John Graham
authors.initials: JG
authors.lastname: Cooper
authors.forename: Thor
authors.initials: T
authors.lastname: Thorsen
authors.forename: Hrafnkell
authors.initials: H
authors.lastname: Thordarson
authors.forename: Eystein S
authors.initials: ES
authors.lastname: Husebye
mesh_terms: D000324:Adrenocorticotropic Hormone; D000328:Adult; D002940:Circadian Rhythm / Q000502:physiology*; D003937:Diagnosis, Differential; D006261:Headache / Q000097:blood / Q000209:etiology / Q000503:physiopathology; D006801:Humans; D006854:Hydrocortisone / Q000097:blood / Q000378:metabolism*; D008297:Male; D010913:Pituitary-Adrenal System / Q000502:physiology; D012463:Saliva / Q000737:chemistry
chemical_list: D000324:Adrenocorticotropic Hormone; D006854:Hydrocortisone