Newcastle Laboratories

Urinary free cortisol, urine

Clinical Background:

Cortisol is the primary glucocorticoid hormone synthesised and secreted by the adrenal cortex. It is essential for life, regulating carbohydrate, protein and lipid metabolism, maintaining blood pre...

Cortisol is the primary glucocorticoid hormone synthesised and secreted by the adrenal cortex. It is essential for life, regulating carbohydrate, protein and lipid metabolism, maintaining blood pressure and inhibiting allergic and inflammatory reactions. Cortisol is synthesised and secreted by the cortex of the adrenal gland under the direction of adrenocorticotropic hormone (ACTH). ACTH is secreted in a circadian pattern by the anterior lobe of the pituitary gland in response to corticotropin releasing hormone (CRH) secretion by the hypothalamus. Increased ACTH levels stimulate cortisol secretion. As levels of cortisol increase they inhibit CRH secretion which subsequently inhibits ACTH secretion and the production of cortisol decreases.Circulating cortisol levels follow a diurnal pattern in healthy individuals with the highest levels seen in the morning after waking and the lowest in the evening. Disorders of the hypothalamic-pituitary-adrenal axis override this diurnal pattern.
Cushing’s syndrome is caused by increased production of cortisol due to either primary or secondary adrenal hyperfunction. Causes of primary adrenal hyperfunction are adrenal tumours and nodular adrenal hyperplasia. Secondary adrenal hyperfunction is caused by pituitary overproduction of ACTH or ectopic production of ACTH/CRH by a tumour. Increased cortisol levels are induced by pregnancy and by stress due to depression, trauma, surgery, hypoglycaemia, alcoholism, uncontrolled diabetes and starvation.

Cortisol circulates largely (90-95%) protein bound to corticosteroid binding globulin (CBG) and albumin. The hormone is metabolised by the liver to form a number of metabolically inactive products, which are excreted in urine mainly in the form of conjugated metabolites. About 1% is excreted unchanged in the urine. This is the urinary "free" cortisol and reflects the concentrations of circulating non protein-bound cortisol.

A 24-hour urinary cortisol measurement is one of the tests used in initial screening for Cushing’s syndrome because it provides an assessment of cortisol production that is not affected by diurnal variation (as is the case for untimed serum cortisol measurements).

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Test Details

  • Discipline:

    Biochemistry

    Biochemistry

  • Specimen Container Adult:

    Urine, 24h (no preservative)

    Urine, 24h (no preservative)

  • Specimen Container Paediatric:

    Urine, 24h (no preservative)

    Urine, 24h (no preservative)

  • Minimum Volume Adult:

    1 mL urine

    1 mL urine

  • Minimum Volume Paediatric:

    1 mL urine

    1 mL urine

  • Special Requirement:

    Accurate timing of the urine collection is required. Keep collection bottle refrigerated between bladder voidings if possible.

    Accurate timing of the urine collection is required. Keep collection bottle refrigerated between bladder voidings if possible.

  • Sample Stability:

    7 days at 4-8°C, 1 month at -20°C

    7 days at 4-8°C, 1 month at -20°C

  • Transport Requirements:

    Ambient

    Ambient

  • Interpretation:

    False-positive elevations of UFC may be seen in a number of conditions such as high fluid intake (>5 litres per day), depression and other psychiatric conditions, alcohol dependence, poorly control...

    False-positive elevations of UFC may be seen in a number of conditions such as high fluid intake (>5 litres per day), depression and other psychiatric conditions, alcohol dependence, poorly controlled diabetes mellitus, physical stress (e.g. pain, surgery), malnutrition, intense chronic exercise.

    False-negatives may occur in renal failure (creatinine clearance less than 60mL/min, with UFC concentrations falling with declining renal filtration rates), cyclical Cushing’s during periods of disease inactivity and in some cases of mild Cushing’s.

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  • Reference Ranges:

    Less than 132 nmol/24h

    Less than 132 nmol/24h

  • Factors Affecting Result:

    Inaccurate timing of 24 hour urine collection will impair the accuracy of estimation of 24hr urine cortisol excretion.

    Exogenous glucocorticoid therapy may suppress endogenous cortisol secretion. A...

    Inaccurate timing of 24 hour urine collection will impair the accuracy of estimation of 24hr urine cortisol excretion.

    Exogenous glucocorticoid therapy may suppress endogenous cortisol secretion. A mass spectrometry assay is now in use, which is less susceptible to interference compared to immunoassay methods.

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  • Routine Contact Name:

    Duty Biochemist

  • Routine Telephone:

    Freeman: 0191 244 8889

    RVI: 0191 282 9719

    Freeman: 0191 244 8889

    RVI: 0191 282 9719

  • Routine Email:

  • Specialist Test:

    Yes

    Yes

  • Specialist Contact Name:

    Endocrine Lab

    Endocrine Lab

  • Specialist Telephone:

    0191 282 4025

    0191 282 4025

Availability:

Available during full access hours
Assayed weekly
Site of analysis: RVI

Turn Around:

2 weeks

Send To:

Department of Blood Sciences

Level 3
Leazes Wing
Royal Victoria Infirmary
Queen Victoria Road
Newcastle upon Tyne
NE1 4LP

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