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Test ID: 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

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.

Interpretation

Most patients with Cushing syndrome have increased 24-hour urinary excretion of cortisol. Further studies, including suppression or stimulation tests, measurement of serum corticotrophin 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. However, many normal individuals may also exhibit a very low 24-hour urinary cortisol excretion with considerable overlap with the values observed in pathological hypocorticalism. Therefore, without other tests, 24-hour urinary cortisol measurements cannot be relied upon for the diagnosis of hypocorticalism.

Analytic Time

2 days (not reported on Sundays)

Day(s) and Time(s) Performed

Monday through Friday; 4 p.m.

Clinical Reference

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

4. Eisenhofer G, Grebe S, Cheung N-K V: Chapter 63 Monoamine-Producing Tumors. In Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. Sixth edition. Edited by N Rafai, AR Horvath, CT Wittwer. Elsevier, 2018. pp 1421

5. Luo A, El Gierari ETM, Nally LM, et al: Clinical utility of an ultrasensitive urinary free cortisol assay by tandem mass spectrometry. Steroids. 2019 Jun;146:65-69. doi: 10.1016/j.steroids.2019.03.014

Method Name

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

Specimen Type

Urine


Necessary Information


24-Hour volume is required.



Specimen Required


Supplies: Urine Tubes, 10-mL (T068)

Submission Container/Tube: Plastic, urine tube

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: See Urine Preservatives-Collection and Transportation for 24-Hour Urine Specimens in Special Instructions for multiple collections.


Specimen Minimum Volume

3 mL

Specimen Stability Information

Specimen Type Temperature Time Special Container
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 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)

 

For SI unit Reference Values, see https://www.mayocliniclabs.com/order-tests/si-unit-conversion.html

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

LOINC Code Information

Test ID Test Order Name Order LOINC Value
CORTU Cortisol, Free, U 43126-2

 

Result ID Test Result Name Result LOINC Value
8546 Cortisol, U 14158-0
TM93 Collection Duration 13362-9
VL47 Urine Volume 3167-4

Urine Preservative Collection Options

Note: The addition of preservative must occur prior to the start of the collection or application of temperature controls must occur during collection.

Ambient

No

Refrigerate

OK

Frozen

OK

50% Acetic Acid

OK

Boric Acid

Preferred

Diazolidinyl Urea

No

6M Hydrochloric Acid

No

6M Nitric Acid

No

Sodium Carbonate

No

Thymol

No

Toluene

No

Mayo Clinic Laboratories | Endocrinology Catalog Additional Information:

mml-adrenal-gonad-pituitary