Does a normal urine free cortisol result rule out Cushing’s syndrome?



March 07, 2015

SAT 379-412-Cushing’s Syndrome

Does a normal urine free cortisol result rule out Cushing’s syndrome?

ST Sharma, LK Nieman

Summary: Researchers conducted this study to assess the diagnostic accuarcy of urine free cortisol (UFC) and 24-hour urine 17-hydroxycorticosteroids (170HCS) in patients with Cushing’s syndrome, concluding that in patients with mild CS, UFC can be falsely normal or only minimally elevated. Further, they found that to help in making a diagnosis and prevent treatment delays, clinicians may consider incorporating multiple collections and use of complimentary screening tests including 24-hour urine 17OHCS and late night salivary cortisol (LNSC) testing.


  • For this retrospective study, researchers included all CS patients evaluated at the National Institutes of Health (NIH) from 2009 to 2014.
  • The screening tests used for CS included UFC, 17OHCS, midnight serum cortisol and low dose (1 mg overnight or 2-day 2 mg/day) dexamethasone suppression test (DST).
  • They defined abnormal as values above reference range for UFC, 17OHCS and LNSC, a midnight serum cortisol ≥7.5 mcg/dL, and post-dexamethasone cortisol values ≥1.8 mcg/dL.
  • Hourly 24-hour sampling for cortisol was performed in a few cases with a mild clinical phenotype and equivocal test results.
  • Researchers measured UFC using liquid chromatography/tandem mass spectrometry (LC-MS/MS), and 17OHCS was measured using colorimetric methodology with Porter-Silber reaction (reported as mg/g of creatinine).
  • For this study, they used the mean of the first two UFC and 17OHCS values (appropriate collection by urine volume and creatinine) obtained within 30 days of initial NIH presentation.


  • In all, 72 patients were diagnosed with CS (aged 18-77 years, 51 females), 51 of whom had CD, 10 had ectopic CS, and 2 had an adrenal source of Cushing’s based on pathology.
  • Biochemical tests such as inferior petrosal sinus sampling (IPSS) suggested ectopic CS, but no tumor was found (occult) in 6 patients.
  • In 2 patients with failed transsphenoidal surgery, IPSS was indicative of a pituitary source, and one patient did not complete evaluation for ACTH-dependent CS.
  • UFC results were available in all patients, 17OHCS in 70, LNSC in 21, midnight serum cortisol in 68, and DST results in 37 patients.
  • UFC was falsely normal in 6 patients and only minimally elevated (<2 x ULN) in 13 patients (normal renal function, no history of cyclicity, all had CD); of these 19 patients, 24-hour 17OHCS was abnormal in all, LNSC was abnormal in 12, midnight serum cortisol was abnormal in 18, and DST was abnormal in 12 patients.
  • Hourly 24-hour sampling for cortisol performed in 3 of these patients revealed abnormal nadir (>7.5 mcg/dL) and mean daily serum cortisol (>9 mcg/dL) levels.


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Does a normal urine free cortisol result rule out Cushing’s syndrome?
ST Sharma, LK Nieman

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