Cortisol Urine Test, Urinary Free, 24-Hour
A Cortisol Urine Test, Urinary Free is used in 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.
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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