Lab

Free Urine Cortisol

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Free Urine Cortisol, 24-hour Urinary Free Cortisol, 24 hour Urine Cortisol, Urine 17-Ketosteroid Excretion, Urine 17-Hydroxysteroid Excretion, 24 Hour Urine Cortisol Test

  • See Also
  1. Cushing's Syndrome
  1. Preferred among 3 first line options for Cushing's Syndrome Screening
    1. See Low-Dose Dexamethasone Suppression Test
    2. See Late-Night Salivary Cortisol (LNSC)
  • Mechanism
  1. Measures Urine 17-Ketosteroid Excretion and Urine 17-Hydroxysteroid Excretion
  • Technique
  1. Collect urine for 24 hours
  2. Start in the morning after first void
  3. Continue to collect urine until the next morning and include the first morning void
  4. Obtain urine Cortisol and Urine Creatinine
  5. Perform at least twice due to variability (discrepant in 50% of samples)
  • Interpretation
  • Normal
  1. Free Urine Cortisol: 10-84 mcg/24 hours (up to 110 mcg/24 hours in some reference ranges)
  • Causes
  • Increased (especially if 4x normal range)
  1. See Serum Cortisol
  2. Cushing's Syndrome
  1. Incorrect urine collection
  2. Pregnancy
  3. Excessive fluid intake (>5 Liters/day)
  4. Pseudo-Cushing's Syndrome
  5. Drug Interactions
    1. Carbamazepine
    2. Fenofibrate
    3. Estrogen
    4. Licorice
    5. Carbenoxolone
  1. Incorrect urine collection
  2. Impaired Renal Function (eGFR <60 ml/min)
  3. Low level Cushing's Syndrome
  • Efficacy
  1. Relies on complete and accurate urine collection
  2. Often falsely normal in adrenal hypercortisolism (use Dexamethasone suppression instead)
  3. Perform at least twice due to variability (discrepant in 50% of samples)
  4. Test Sensitivity: 80 to 98%
  5. Test Specificity: 45 to 98%
  • References
  1. Elamin (2008) J Clin Endocrinol Metab 93(5):1553-62 +PMID: 18334594 [PubMed]
  2. Galm (2020) J Clin Endocrinol Metab 105(6):dgaa105 +PMID: 32133504 [PubMed]
  3. Maness (2024) Am Fam Physician 110(3): 270-80 [PubMed]