title: Spectral effect: each population must have its own normal midnight salivary cortisol reference values determined.
abstract: BACKGROUND
  The mesurement of midnight salivary cortisol provides the most sensitive method for screening of Cushing's sendrome. However the clinical significance of spectral error is the requirement for determination of normal reference values in each population for each test, which will be used as the diagnostic method. Salivary cortisol levels may be affected by individual factors such as nutrition, sleep, medication, activity, and gender. Being a non-invasive method, midnight salivary cortisol (MSC) has been used as a valuable indicator of free plasma cortisol.
  
  
  METHODS
  Midnight salivary cortisol was assessed in randomly selected 100 Turkish patents who underwent to a detailed physical examination. Saliva samples were collected at 00:00 to plastic tubes with the help of plastic pipettes, without brushing their teeth, but after rinsing their mouth. Salivary cortisol was measured with luminescense immunoassay kit. Differences and correlations were analysed.
  
  
  RESULTS
  The mean midnight salivary cortisol of the healthy population was 0.21 ±0.03 µg/dl. Body mass index, age, sex, smoking, exercise, educational status alcohol, had no effect on the MSC.
  
  
  CONCLUSIONS
  Consequently, normal salivary cortisol reference ranges must be used for different assays and different populations in order to evaluate more accurately pituitary-adrenal axis pathology in clinical practice.
authors.affiliation: Bakırkoy Dr. Sadi Konuk Training Hospital, Endocrinology and Metabolism, Istanbul, Turkey.
authors.forename: Meral
authors.initials: M
authors.lastname: Mert
authors.forename: Refik
authors.initials: R
authors.lastname: Tanakol
authors.forename: Hande
authors.initials: H
authors.lastname: Karpuzoglu
authors.forename: Semra
authors.initials: S
authors.lastname: Abbasoglu
authors.forename: Sema
authors.initials: S
authors.lastname: Yarman
authors.forename: Harika
authors.initials: H
authors.lastname: Boztepe
authors.forename: Faruk
authors.initials: F
authors.lastname: Alagol
keywords: midnight salivary cortisol; normal reference range; spectral effect