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HelpTest Code CORTU Cortisol, Free, 24 Hour, Urine
Reporting Name
Cortisol, Free, UUseful 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
UrineNecessary 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 |
Special Instructions
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
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 (h) | 13362-9 |
| VL47 | Volume (mL) | 3167-4 |
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.
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.
Liquid chromatography tandem mass spectrometry eliminates analytical interferences including carbamazepine (Tegretol) and synthetic corticosteroids.
Kidney 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.
Report Available
2 to 7 daysSpecimen Retention Time
14 daysReject Due To
All specimens will be evaluated at Mayo Clinic Laboratories for test suitability.Method Name
Liquid Chromatography Tandem Mass Spectrometry (LC-MS/MS)
Secondary ID
8546Forms
If not ordering electronically, complete, print, and send a Renal Diagnostics Test Request (T830) with the specimen.