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Cortisol, Free, 24-Hour Urine

Measures the free (active) cortisol your body clears in urine over a full day. It is one of the standard first tests when Cushing syndrome is a question.

AI-drafted. Awaiting verificationAlso called UFC, 24h UFC, UFC-24LOINC 2147-7

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What it is

Most cortisol in blood is attached to a carrier protein. The small free part passes through the kidneys into urine. A 24-hour urine collection adds up this free cortisol over a whole day, which smooths out the ups and downs that a single blood test can show. Because it measures only the free part, it isn't thrown off when estrogen raises the carrier protein. The result is given in micrograms (µg) of cortisol per 24 hours.

Why it matters

Clinicians use it to look into Cushing syndrome, a condition in which the body has too much cortisol for a long time. The Endocrine Society recommends at least two collections, because levels can swing from one day to the next. A result above your lab's range does not confirm Cushing syndrome. Stress, heavy fluid intake, pregnancy, some medicines, and conditions such as depression, alcohol misuse, obesity and poorly controlled diabetes can all raise it, usually to less than about 4 times the upper limit.

If it’s low

A low or in-range result is common and does not on its own rule anything in or out. Missed urine during the collection and reduced kidney function both lower the result. This test isn't used to look into low cortisol.

Common causes

  • A collection that missed some urine
  • Reduced kidney function (creatinine clearance below about 60 mL/min)
  • Normal variation between people
  • Cortisol excess that comes and goes, if the collection fell on a quiet day

What can help

  • Ask whether your urine creatinine suggests the collection was complete
  • Ask whether your kidney function could have affected the result

If it’s high

A result above your lab's range has many everyday explanations, including a collection that was too large, drinking a lot of fluid, stress, pregnancy and some medicines. Less often, it is linked to Cushing syndrome, where the body has too much cortisol over a long time. One result can't tell these apart, so clinicians usually repeat the collection and add other tests.

Common causes

  • Drinking a lot of fluid (5 liters or more a day), or collecting more than 24 hours of urine
  • Physical or emotional stress, or acute illness
  • Pregnancy, mostly in the second and third trimesters
  • Medicines such as carbamazepine, and steroid products that some methods read as cortisol
  • Depression, anxiety, alcohol misuse, obesity or poorly controlled diabetes, which can mildly raise cortisol
  • Cushing syndrome (uncommon)

What can help

  • Ask whether your collection was complete and the right length, and whether a repeat is needed
  • Tell your clinician about every steroid pill, injection or cream you use, and about your other medicines
  • Ask whether another test, such as late-night saliva cortisol, fits your situation

Usual ranges

What labs print as the reference range, by who was tested. Ranges differ a little between labs, so the range on your own report is the one your result is judged against.

The usual range depends on sex and age. Choose women or men to see the one that applies.

See Urine free cortisol by age and sex, with the U.S. survey numbers where they exist.

What can affect your result

  • Completeness and length of the collection
  • Fluid intake: 5 liters a day or more raises it
  • Kidney function: lower filtration lowers the result
  • Pregnancy: rises in the second and third trimesters
  • Medicines and steroid products, including some creams
  • Method: LC-MS/MS is the most specific, and immunoassays can pick up other steroids, so each method has its own range
  • Incomplete or over-long collections: missed urine gives a falsely low result and extra urine can raise it. Labs often check urine creatinine to judge whether the collection was complete.
  • Drinking a lot of fluid (5 liters a day or more) raises urine free cortisol.
  • Reduced kidney function lowers it, starting when creatinine clearance falls below about 60 mL/min.
  • Pregnancy: normal in the first trimester, then rising, to up to about 3 times by the end of pregnancy.
  • Conditions that raise cortisol without Cushing syndrome (depression, anxiety, alcohol misuse, obesity, poorly controlled diabetes) can mildly raise it, usually to less than about 4 times the upper limit.
  • Carbamazepine can raise it. Fenofibrate can raise it on HPLC methods. Steroid medicines, including some skin creams, can read as cortisol on some methods, so tell your clinician about every steroid product you use.
  • Containers and storage differ between labs (ARUP wants the collection kept cold with no preservative or acid, while Labcorp accepts boric acid or HCl), so use the container and instructions from your own lab.

A full 24-hour collection. It starts by emptying the bladder at a set time in the morning and throwing that urine away. Labcorp uses 8 a.m. Shows average cortisol output over the 24 hours of the collection. Cortisol excess that comes and goes can be missed on a quiet day.

When to talk to a clinician

Contact the clinician who ordered the test if your result is outside your lab's range. They will usually want to repeat it before drawing conclusions. If you feel very unwell, for example with severe weakness, confusion, trouble breathing or chest pain, call 911 or your local emergency number.

Questions you could ask

  • Does my lab use mass spectrometry, and what range does it use?
  • Was my collection complete and the right length?
  • Could any medicine, steroid cream, pregnancy or heavy fluid intake have affected it?
  • Should we repeat the collection or try another test, such as late-night saliva cortisol?
  • Could an incomplete collection or my kidney function have affected this result?

Questions people ask

How do I collect a 24-hour urine sample?

Follow the instructions from the lab that gave you the container, because they differ. The Endocrine Society's general approach is to empty your bladder in the morning and throw that urine away, then collect all urine for the next 24 hours, including the first urine the following morning. Keep it cool as directed, and avoid drinking unusually large amounts of fluid.

Why might my clinician ask for more than one collection?

Cortisol output can vary from day to day, and a collection can be incomplete. The Endocrine Society recommends at least two urine free cortisol collections when this test is used to look into Cushing syndrome.

How do I convert µg/24 h to nmol/24 h?

Multiply µg/24 h by 2.76, so 45 µg/24 h is about 124 nmol/24 h. To go the other way, multiply nmol/24 h by 0.3625.

Show the science and sources

Units

  • 1 µg/24 h = 1 µg/24 h
  • 1 µg/24 h = 2.759 nmol/24 h

Open the Urine free cortisol unit converter

For clinicians and researchers

Urine free cortisol (UFC) reflects the fraction of plasma free cortisol that is filtered unchanged by the kidney, so unlike serum cortisol it is not affected by estrogen-driven changes in cortisol-binding globulin. The 2008 Endocrine Society guideline lists UFC (at least two measurements) among four recommended initial tests for Cushing syndrome and uses the assay's upper limit of normal as the positive criterion. It notes that non-Cushing hypercortisolism rarely goes above about 4 times normal. In pregnancy, UFC is normal in the first trimester and rises up to 3-fold by term, so only second- or third-trimester values above 3 times the upper limit are suggestive. In adrenal incidentaloma UFC appears less sensitive than the 1-mg dexamethasone test or late-night salivary cortisol, and it falls linearly once creatinine clearance is below 60 mL/min, so the guideline suggests the 1-mg dexamethasone test instead in severe renal failure. LC-MS/MS avoids the cross-reactivity seen with immunoassays. Reference limits differ by lab (adults: Labcorp 5 to 64 µg/24 h in men and 6 to 42 in women, ARUP up to 60 and up to 45, Quest 4.0 to 50.0 with no sex split). A per-24-hour result needs a complete collection; ARUP also reports cortisol per gram of creatinine for collections of uncertain length or volume. Conversion: µg/24 h × 2.76 = nmol/24 h (cortisol molecular weight 362.5). Concentration results in µg/L (LOINC 33346-8) are a different measurement and are not converted here.

LOINC 2147-7 (primary), 14676-1. Specimen: urine-24h.

Sources

  1. Cortisol, Urinary Free (test 004432), Labcorp
  2. Cortisol Urine Free by LC-MS/MS (test 0097222), ARUP Laboratories
  3. Cortisol, Free, 24-Hour Urine with Creatinine, LC/MS/MS (Quest test 11280), Quest Diagnostics, as listed in the Compunet Clinical Laboratories test directory
  4. The Diagnosis of Cushing's Syndrome: An Endocrine Society Clinical Practice Guideline, Journal of Clinical Endocrinology & Metabolism (2008)
  5. Cortisol (PubChem CID 5754), NCBI PubChem

AI-drafted. Awaiting verification. Last reviewed 2026-10-03. How we build and check these pages.

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