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Test ID CORTU Cortisol, Free, 24 Hour, Urine

Secondary ID

8546

Useful For

Preferred screening test for Cushing syndrome

 

Diagnosis of pseudo-hyperaldosteronism due to excessive licorice consumption

 

This test has limited usefulness in the evaluation of adrenal insufficiency

Method Name

Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS)

Reporting Name

Cortisol, Free, U

Specimen Type

Urine

Container/Tube: Plastic, 10-mL urine tube (T068)

Specimen Volume: 5 mL

Collection Instructions:

1. Collect urine for 24 hours.

2. Add 10 g of boric acid as preservative at start of collection.

Additional Information:

1. 24-Hour volume is required.

2. See Urine Preservatives in Special Instructions for multiple collections.

 

Urine Preservative Collection Options

Ambient

No

Refrigerated

Yes

Frozen

Yes

6N HCl

No

50% Acetic Acid

Yes

Na2CO3

No

Toluene

Yes

6N HNO3

No

Boric Acid

Preferred

Thymol

No

 

Specimen Minimum Volume

3 mL

Specimen Stability Information

Specimen Type Temperature Time
Urine Refrigerated (preferred) 14 days
  Frozen  28 days
  Ambient  7 days

Clinical Information

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) in the urine 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-tandem 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.

Reference Values

0-2 years: not established

3-8 years: 1.4-20 mcg/24 hours

9-12 years: 2.6-37 mcg/24 hours

13-17 years: 4.0-56 mcg/24 hours

≥18 years: 3.5-45 mcg/24 hours

 

Use the factor below to convert from mcg/24 hours to nmol/24 hours:

 

Conversion factor

Cortisol: mcg/24 hours x 2.76=nmol/24 hours (molecular weight=362.5)

Cautions

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.

 

This test has limited usefulness in the evaluation of adrenal insufficiency.

 

This methodology (liquid chromatography-tandem mass spectrometry) eliminates analytical interferences including carbamazepine (Tegretol) and synthetic corticosteroids.

 

Renal disease (decreased excretion) may cause falsely low 24-hour urinary free cortisol values.

 

Improper collection may alter results. For example, a missed morning collection may result in false-negative tests; an extra morning collection (ie, >24 hours) may give false-positive results.

 

Twenty-four hour urinary free cortisol values may be elevated to twice the upper limit of the normal range during pregnancy.

 

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

Day(s) Performed

Monday through Friday; 1 p.m.

Report Available

2 days (not reported on Sundays)

Performing Laboratory

Mayo Medical Laboratories in Rochester

Test Classification

This test was developed and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the U.S. Food and Drug Administration.

CPT Code Information

82530

NY State Approved

Yes