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Test Code CORTU Cortisol, Free, 24 Hour, Urine

Reporting Name

Cortisol, Free, U

Useful For

Preferred screening test for Cushing syndrome

 

Diagnosis of pseudo-hyperaldosteronism due to excessive licorice consumption

 

Test may not be useful in the evaluation of adrenal insufficiency.

Performing Laboratory

Mayo Clinic Laboratories in Rochester

Specimen Type

Urine


Necessary Information


24-Hour volume (in milliliters) is required.



Specimen Required


Supplies: Urine Tubes, 10-mL (T068)

Submission Container/Tube: Plastic urine tube

Specimen Volume: 5 mL

Collection Instructions:

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

2. Collect urine for 24 hours and record the total volume.

Additional Information: See Urine Preservatives-Collection and Transportation for 24-Hour Urine Specimens for multiple collections.


Specimen Minimum Volume

3 mL

Specimen Stability Information

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

Reference Values

0-2 years: Not established

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

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

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

≥18 years: 3.5-45 mcg/24 h

 

For International System of Units (SI) conversion for Reference Values, see www.mayocliniclabs.com/order-tests/si-unit-conversion.html.

Day(s) Performed

Monday through Friday

Test Classification

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

CPT Code Information

82530

Clinical Information

Cortisol is a steroid hormone synthesized from cholesterol through multienzyme pathway in the adrenal glands. It is the primary glucocorticoid in humans and acts as a gene transcription factor influencing a multitude of cellular responses in nearly all tissues. Cortisol plays a critical role in glucose metabolism, maintenance of vascular tone, immune response regulation, and in the physiologic response to stress. Its production is regulated by hypothalamic-pituitary feedback.

 

Only a small percentage of circulating cortisol is biologically active (free), with the majority of cortisol inactive because it is protein bound. As plasma cortisol concentrations increase, free cortisol (ie, unconjugated cortisol or hydrocortisone) also increases and is filtered by the glomeruli. Urinary free cortisol (UFC) in the urine correlates well with plasma free cortisol concentrations and reflects excretion of the circulating, biologically active, free cortisol associated with the signs and symptoms of hypercortisolism.

 

Urinary free cortisol testing is sensitive for the various types of adrenocortical dysfunction, particularly hypercortisolism (Cushing syndrome). 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 from substances such as carbamazepine (Tegretol) and synthetic corticosteroids, which can affect immunoassay-based cortisol results.

Report Available

2 to 7 days

Reject Due To

  All specimens will be evaluated at Mayo Clinic Laboratories for test suitability.

Method Name

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

Forms

If not ordering electronically, complete, print, and send a Renal Diagnostics Test Request (T830) with the specimen.