Test Details
Methodology
Liquid chromatography/tandem mass spectrometry (LC/MS-MS)
Result Turnaround Time
4 - 6 days
Turnaround time is defined as the usual number of days from the date of pickup of a specimen for testing to when the result is released to the ordering provider. In some cases, additional time should be allowed for additional confirmatory or additional reflex tests. Testing schedules may vary.
Use
The diagnosis of Cushing syndrome (CS) requires evidence of cortisol hypersecretion. While serum cortisol levels fluctuate unpredictably and are strongly dependent on concurrent cortisol-binding globulin (CBG) levels, a 24-hour urine specimen integrates the cortisol production for an entire day and is not affected by CBG. Urinary cortisol reflects the portion of serum-free cortisol filtered by the kidney, and correlates well with cortisol secretion rate.
The most common causes of CS are pituitary adenoma (65% to 70%), adrenal tumor (15% to 20%), and ectopic CS (10% to 15%).
Special Instructions
State 24-hour volume.
Limitations
Not useful in the evaluation of adrenal insufficiency (AI). Results in AI overlap with normal ranges. Increased in pregnancy and with oral contraceptives. Increased excretion may be found with pseudo-Cushing syndrome, trauma, or infection.2 Tetracyclines may cause false elevation of results.
This test was developed and its performance characteristics determined by LabCorp. It has not been cleared or approved by the Food and Drug Administration.
Custom Additional Information
This test is useful in the initial evaluation of patients with suspected Cushing syndrome (CS).1,2 Patients with CS usually have urine free cortisol >100 μg/24 hours, but there is wide variation and no single cutoff can be used safely. If the 24-hour urine free cortisol is elevated, additional testing is indicated to differentiate among pituitary-dependent CS, pituitary-independent CS, and pseudo-Cushing syndrome.2
Some patients with an elevated 24-hour urine cortisol do not have Cushing syndrome and are often classified as pseudo-Cushing syndrome. Establishing this diagnosis requires additional testing which includes the low-dose dexamethasone suppression test, the CRH stimulation test, or a protocol that combines them both.3
The diagnosis of CS requires a meticulous history and physical examination,2 and these should precede a biochemical evaluation.
Specimen Requirements
Specimen
Urine (24-hour)
Volume
100 mL aliquot
Minimum Volume
10 mL aliquot (Note: This volume does not allow for repeat testing.)
Container
Plastic urine container
Collection Instructions
Instruct the patient to void at 8 AM and discard the specimen. Then collect all urine including the final specimen voided at the end of the 24-hour collection period (ie, 8 AM the next morning) in a plastic bottle. Screw the lid on securely. (It is acceptable to collect cortisol with boric acid or HCl preservative.)
Stability Requirements
Temperature | Period |
|---|---|
Room temperature | 14 days |
Refrigerated | 14 days |
Frozen | 14 days |
Freeze/thaw cycles | Stable x3 |
Reference Range
Age | Male (μg/24h) | Female (μg/24h) |
|---|---|---|
0 days to 1 year | Not established | Not established |
2 to 5 years | 2 – 16 | 2 – 16 |
6 to 11 years | 4 – 28 | 4 – 24 |
12 years | 4 – 36 | 4 – 36 |
13 to 17 years | 6 – 45 | 6 – 42 |
18 to 80 years | 5 – 64 | 6 – 42 |
>80 years | 3 – 49 | 3 – 49 |
Storage Instructions
Room temperature
References
Footnotes
LOINC® Map
| Order Code | Order Code Name | Order Loinc | Result Code | Result Code Name | UofM | Result LOINC |
|---|---|---|---|---|---|---|
| 004432 | Cortisol, Urinary Free | 43126-2 | 004433 | Cortisol,F,ug/L,U | ug/L | 33346-8 |
| 004432 | Cortisol, Urinary Free | 43126-2 | 004434 | Cortisol,F,ug/24hr,U | ug/24 hr | 2147-7 |
| Order Code | 004432 | |||||
| Order Code Name | Cortisol, Urinary Free | |||||
| Order Loinc | 43126-2 | |||||
| Result Code | 004433 | |||||
| Result Code Name | Cortisol,F,ug/L,U | |||||
| UofM | ug/L | |||||
| Result LOINC | 33346-8 | |||||
| Order Code | 004432 | |||||
| Order Code Name | Cortisol, Urinary Free | |||||
| Order Loinc | 43126-2 | |||||
| Result Code | 004434 | |||||
| Result Code Name | Cortisol,F,ug/24hr,U | |||||
| UofM | ug/24 hr | |||||
| Result LOINC | 2147-7 |