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Cortisol assays & diagnostic laboratory procedures


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Cortisol assays & diagnostic laboratory procedures

  1. 1. M.Prasad Naidu MSc Medical Biochemistry, Ph.D,.
  2. 2. Introduction  Cortisol level measurement is used in the assessment of adrenal,pituitary & hypothalamic function & is especially important in the diagnosis of Cushing’s syndrome & Addison’s disease.  Total serum cortisol,24 hr urinary free cortisol,salivary free cortisol are measured.
  3. 3. Physiology  Cortisol is a glucocorticoid hormone secreted by the zona fasciculata of adrenal cortex.  Cortisone & corticosterone are the other glucocorticoids.  CRH(corticotropin releasing hormone) &ACTH(adrenocorticotrophic hormone) stimulate cortical secretion.  These steroid hormones act through intracellular messengers & increase the rate of transcription.
  4. 4. Contd-------  70% of cortisol in blood is bound to CBG(cortisol binding globulin).  20% bound to albumin.  The rest is free, which is biologically active.  Metabolism takes place in liver.  These are first reduced & excreted as their glucuronides or sulphates in urine.
  5. 5. Contd  Cortisol levels in blood are characterised by Circadian rhythm with a morning maximum,  Declining levels throughout the daytime  A period of low concentration around midnight & rise after the first few hours of sleep  This circadian rhythm has been demonstrated in plasma,than in urine & saliva.
  6. 6. Functions This steroid plays pivotal role in  Energy metabolism  Maintenance of electrolyte balance & blood pressure,  Immune modulation & stress response,  Cell proliferation & differentiation,  Memory & cognitive functions
  7. 7. Laboratory cortisol assays Serum total cortisol  Radioimmunoassay  Liquid chromatography  HPLC  Fluorescence polarisation immunoassay Serum free cortisol assays  Coolen’s method  Ultrafiltration Disadvantages  Invasive procedure  Stress induced rise of cortisol level
  8. 8. Urine free cortisol assay  RIA  Immunoassays  Liquid chromatography Disadvantages Pretreatment of urine sample
  9. 9. Salivary cortisol assays RIA Immunoassays Liquid chromatography Advantages Noninvasive procedure