M.Prasad NaiduMSc Medical Biochemistry,

Ph.D,.

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.

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.

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.

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.

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

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

Urine free cortisol assay RIA Immunoassays Liquid chromatography

DisadvantagesPretreatment of urine sample

Salivary cortisol assaysRIAImmunoassaysLiquid chromatography

AdvantagesNoninvasive procedure