LabCorp Test

Cortisol Urine Test, Urinary Free, 24-Hour

Quick Overview

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.

Test #004432


Availability: In stock

Also Known As Urinary Free Cortisol
Preparation No fasting required. Urinate at 8am and discard the specimen. Then collect all urine in 24-hour period, ending with final collection at 8am the next morning. Refrigerate the collected urine between all voidings or keep it in a cool place. Screw the lid on securely. Transport the specimen promptly to the laboratory. Container must be labeled with full name, date and time collection started, and date and time collection finished.
Test Results 3-4 days. May take longer based on weather, holiday or lab delays.

Walk-In Lab's urinary free cortisol test helps with the initial evaluation of patients with suspected Cushing syndrome (CS). 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 typically needed to determine whether a patient has pituitary-dependent CS, pituitary-independent CS or pseudo-Cushing syndrome.

Pseudo-Cushing syndrome occurs when patients with an elevated 24-hour urine cortisol do not have Cushing syndrome. This diagnosis requires additional testing which includes the CRH stimulation test, the low-dose dexamethasone suppression test or a protocol that combines both.

A meticulous history and physical examination are required when diagnosing CS, and should be performed prior to any biochemical evaluations like a urinary free cortisol test.

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