Cortisol assays & diagnostic laboratory procedures

Cortisol assays & diagnostic laboratory procedures

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  M.Prasad Naidu MSc MedicalBiochemistry, Ph.D,.
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  Introduction  Cortisol levelmeasurement 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.
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  Physiology  Cortisol isa 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.
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  Contd-------  70% ofcortisol 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.
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  Contd  Cortisol levelsin 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.
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  Functions This steroid playspivotal role in  Energy metabolism  Maintenance of electrolyte balance & blood pressure,  Immune modulation & stress response,  Cell proliferation & differentiation,  Memory & cognitive functions
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  Laboratory cortisol assays Serumtotal 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
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  Urine free cortisolassay  RIA  Immunoassays  Liquid chromatography Disadvantages Pretreatment of urine sample
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  Salivary cortisol assays RIA Immunoassays Liquidchromatography Advantages Noninvasive procedure