Cortisol, Urinary Free
Cortisol, Urinary Free | | | |
| Number | | 004432 |
| CPT | | 82530 |
| Related Information | | Urine Testing: Preservative Quick Reference
Chart |
| Synonyms | | Urinary Free Cortisol |
| Special Instructions | | State 24-hour volume. |
| Specimen | | Urine (24-hour) |
| Volume | | 100 mL aliquot |
| Minimum Volume | | 10 mL aliquot |
| Container | | Plastic urine container |
| Collection | | 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 containing
1 g boric acid per liter of urine. Mix well. Screw the lid
on securely. (It is acceptable to collect cortisol with a
HCl preservative or without a preservative.) |
| Storage Instructions | | Refrigerate during collection and store refrigerated. The addition of preservative or refrigeration must occur within 4 hours of completion of the collection. |
| Reference Interval | | Pediatrics1 and adults: - 0-1 year: not established
- 2-11 years: 1-21 μg/24 hours
- 12-16 years: 2-38 μg/24 hours
- Older than 16 years: 0-50 μg/24 hours
|
| 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 the ectopic CS (10%
to 15). |
| 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. |
| Methodology | | Liquid Chromatography Tandem Mass Spectrometry (LC/MS/MS) |
| 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 ug/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 included 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 examiniation,2
and these should precede a biochemical evaluation. |
| Footnotes | |
- Watts, NB and Keffer JH,"Adrenal Cortex"
Practical Endocrinology, 4th ed, Philadelphia, PA:
Lea & Febiger, 1989, 91-120.
- Orth DN, "Cushing's Syndrome" N Engl J
Med, 1995, 332(12):791-803 (published erratum appears
in N Engl J Med, 1995, 332:1527).
- Yanovski JA, Cutler GB, Chrousos GP, et
al, "Corticotropin-releasing hormone stimulation following
low-dose dexamethasone administration, a new test to
distinguish cushing's syndrome from pseudo-cushing's
states." JAMA 1993, 269(17):2232-2238.
|
| References | | Canalis E, Reardon GE, Caldarella AM. A
more specific liquid-chromatographic method for free
cortisol in urine. Clin Chem. 1982;
28(12):2418-2420. |
|