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Interpretive Handbook

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Test 82920 :
Cortisol, Free, Random, Urine

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Cortisol is a steroid hormone synthesized from cholesterol by a multienzyme cascade in the adrenal glands. It is the main glucocorticoid in humans and acts as a gene transcription factor influencing a multitude of cellular responses in virtually all tissues. Cortisol plays a critical role in glucose metabolism, maintenance of vascular tone, immune response regulation, and in the body's response to stress. Its production is under hypothalamic-pituitary feedback control.

 

Only a small percentage of circulating cortisol is biologically active (free), with the majority of cortisol inactive (protein bound). As plasma cortisol values increase, free cortisol (ie, unconjugated cortisol or hydrocortisone) increases and is filtered through the glomerulus. Urinary free cortisol (UFC) correlates well with the concentration of plasma free cortisol. UFC represents excretion of the circulating, biologically active, free cortisol that is responsible for the signs and symptoms of hypercortisolism.

 

UFC is a sensitive test for the various types of adrenocortical dysfunction, particularly hypercortisolism (Cushing syndrome). A measurement of 24-hour UFC excretion, by liquid chromatography-tandom mass spectrometry (LC-MS/MS), is the preferred screening test for Cushing syndrome. LC-MS/MS methodology eliminates analytical interferences including carbamazepine (Tegretol) and synthetic corticosteroids, which can affect immunoassay-based cortisol results.

Useful For Suggests clinical disorders or settings where the test may be helpful

Investigating suspected hypercortisolism when a 24-hour collection is prohibitive (ie, pediatric patients)

Interpretation Provides information to assist in interpretation of the test results

Most patients with Cushing syndrome have increased 24-hour urinary excretion of cortisol. Further studies, including suppression or stimulation tests, measurement of serum corticotropin (adrenocorticotropic hormone) concentrations, and imaging are usually necessary to confirm the diagnosis and determine the etiology.

 

Values in the normal range may occur in patients with mild Cushing syndrome or with periodic hormonogenesis. In these cases, continuing follow-up and repeat testing are necessary to confirm the diagnosis.

 

Patients with Cushing syndrome due to intake of synthetic glucocorticoids should have suppressed cortisol. In these circumstances a synthetic glucocorticoid screen might be ordered (SGSU / Synthetic Glucocorticoid Screen, Urine).

 

Suppressed cortisol values may also be observed in primary adrenal insufficiency and hypopituitarism. The optimal specimen type for evaluation of primary adrenal insufficiency and hypopituitarism is serum (CORT / Cortisol, Serum).

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

Random urine cortisol results are less reliable than results obtained from properly collected and complete 24-hour urine specimens, which are not affected by diurnal variations in cortisol levels.

 

Acute stress (including hospitalization and surgery), alcoholism, depression, and many drugs (eg, exogenous cortisone, anticonvulsants) can obliterate normal diurnal variation, affect response to suppression/stimulation tests, and increase baseline levels.

 

Liquid chromatography-tandom mass spectrometry methodology eliminates analytical interferences including carbamazepine (Tegretol) and synthetic corticosteroids.

 

Random urine specimens may yield falsely elevated values when patients have a high urinary output.

 

Renal disease (decreased clearance) may cause falsely low values.

 

Values may be elevated to twice normal in pregnancy.

 

Patients with exogenous Cushing syndrome caused by ingestion of hydrocortisone will not have suppressed cortisol values.

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.

Males

0-2 years: 3.0-120 mcg/g creatinine

3-8 years: 2.2-89 mcg/g creatinine

9-12 years: 1.4-56 mcg/g creatinine

13-17 years: 1.0-42 mcg/g creatinine

> or =18 years: 1.0-119 mcg/g creatinine

 

Females

0-2 years: 3.0-120 mcg/g creatinine

3-8 years: 2.2-89 mcg/g creatinine

9-12 years: 1.4-56 mcg/g creatinine

13-17 years: 1.0-42 mcg/g creatinine

> or =18 years: 0.7-85 mcg/g creatinine

 

Use the conversion factors below to convert each analyte from mcg/g creatinine to nmol/mol creatinine.

 

Conversion factor

Cortisol: mcg/g creatinine x 413=nmol/mol creatinine

 

Cortisol molecular weight=362.5

Creatinine molecular weight=149.59

Clinical References Provides recommendations for further in-depth reading of a clinical nature

1. Findling JW, Raff H: Diagnosis and differential diagnosis of Cushing's syndrome. Endocrinol Metab Clin North Am 2001;30:729-747

2. Boscaro M, Barzon L, Fallo F, Sonino N: Cushing's syndrome. Lancet 2001;357:783-791

3. Taylor RL, Machacek D, Singh RJ: Validation of a high-throughput liquid chromatography-tandem mass spectrometry method for urinary cortisol and cortisone. Clin Chem 2002;48:1511-1519


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