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Cortisol

The main stress hormone made by your adrenal glands. It follows a daily rhythm, so the time of your blood draw matters when reading the result.

AI-verified against cited sources. Awaiting expert reviewAlso called CORTLOINC 2143-6

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What it is

Cortisol is a hormone made by the adrenal glands, two small glands that sit above your kidneys. It helps your body respond to stress, manage blood sugar and blood pressure, and keep inflammation in check. A signal from your brain, called ACTH, tells the adrenal glands how much to make. Cortisol is highest in the early morning and falls through the day, reaching its lowest point around bedtime.

Why it matters

Clinicians use cortisol to look at whether the adrenal and pituitary glands are making too much or too little of this hormone. Either can affect energy, weight, blood pressure and blood sugar. A single blood result is only a snapshot. It depends on the time of day, stress, sleep, illness and medicines, so it is usually read together with other tests, such as ACTH.

If it’s low

A low morning result can be a sign that the adrenal glands or the pituitary gland aren't making enough cortisol. It also has simpler explanations, such as a sample drawn in the afternoon when levels are normally lower, or steroid medicines that quiet your body's own production. Clinicians usually follow a low morning result with an ACTH test, and often a stimulation test, before drawing any conclusion.

Common causes

  • A blood draw in the afternoon or evening, when levels are normally lower
  • Taking, or recently stopping, steroid medicines such as prednisone
  • Low levels of the proteins that carry cortisol in the blood
  • Addison disease (primary adrenal insufficiency), which is uncommon
  • Pituitary or hypothalamus problems that lower ACTH (secondary adrenal insufficiency)
  • Congenital adrenal hyperplasia, a rare inherited difference in cortisol-making enzymes

What can help

  • Ask your clinician about follow-up testing, such as ACTH or a stimulation test
  • Bring a list of every steroid medicine you take or recently stopped
  • Ask whether the test should be repeated in the morning

If it’s high

A result above your lab's range for the time of day it was drawn has many everyday explanations. Estrogen (from birth control pills, hormone therapy or pregnancy) raises the cortisol measured in blood without raising the active part. Stress, poor sleep, illness and steroid medicines can also push it up. Less often, high cortisol is linked to Cushing syndrome, where the body has too much cortisol for a long time. One result can't tell these apart, so clinicians usually repeat the test or add others.

Common causes

  • Estrogen from birth control pills, hormone therapy or pregnancy
  • Physical or emotional stress, short sleep, or acute illness, including a hospital stay or surgery
  • A blood draw at a different time of day than the range assumes
  • Steroid medicines such as prednisone or prednisolone, which some tests read as cortisol
  • Alcohol misuse, depression, or some medicines such as anti-seizure drugs
  • Cushing syndrome (uncommon)

What can help

  • Tell your clinician about every medicine you use, including steroid pills, injections and birth control
  • Ask whether the draw time and the type of test (blood, saliva or 24-hour urine) fit your question
  • Rest before the draw if your clinician asks, since stress and hard exercise can raise cortisol

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.

We don’t have a usual range for adults.

If this applies to you

Cortisol means a little more for some people. Open the one that fits you.

Endurance athlete

The IOC lists a raised resting morning cortisol as a possible sign of REDs. It is a newer sign that the IOC doesn't yet count in its score. Physical stress, steroid medicines and some other conditions can raise it too, so it is read alongside everything else.

Blood tests for endurance athletes

What can affect your result

  • Time of day: levels peak in the early morning, are roughly half as high by late afternoon, and are lowest around midnight
  • Estrogen: birth control pills, hormone therapy and pregnancy raise total cortisol
  • Stress, illness and hard exercise can raise it
  • Steroid medicines such as prednisone can read as cortisol on some immunoassays
  • Assay method: immunoassay and LC-MS/MS ranges differ, so compare results from the same method
  • High-dose biotin supplements can interfere with some assays
  • Draw time: results are read against the time of day the blood was drawn, because cortisol follows a daily rhythm.
  • Estrogen from birth control pills, hormone therapy or pregnancy raises the carrier protein (CBG) and so raises total cortisol without raising the active, unbound part.
  • Prednisone and prednisolone can read as cortisol on some immunoassays (Mayo reports 41% cross-reactivity for prednisolone on its assay). LC-MS/MS does not have this problem.
  • Acute stress or illness, surgery, alcohol misuse, depression and some medicines (for example anti-seizure drugs) can flatten the daily rhythm and raise baseline levels.
  • High-dose biotin (vitamin B7) can interfere with some assays; Labcorp advises stopping biotin at least 72 hours before the draw unless your clinician says otherwise.
  • Rarely, antibodies to mouse proteins (heterophile antibodies) can distort an immunoassay result.

Early morning (about 7–9 a.m.) is the usual time. Some clinicians also ask for a sample around 4 p.m. Labs use a different range for each, so the draw time matters. Cortisol is released in pulses and follows a daily rhythm, so a single result is a snapshot of that moment rather than a long-term average.

When to talk to a clinician

Contact the clinician who ordered the test if your lab flagged the result or if you take steroid medicines. Clinicians usually look further at a low morning result: Mayo Clinic Laboratories suggests more testing when an 8 a.m. value is under 10 µg/dL (276 nmol/L) and there are symptoms of low cortisol, and the Endocrine Society treats a morning value under 5 µg/dL (140 nmol/L), read together with ACTH, as a preliminary sign that needs confirming with a stimulation test. Seek urgent care for severe weakness, fainting, severe belly pain, vomiting or confusion, particularly if you take or recently stopped steroid medicines. Call 911 or your local emergency number if you feel very unwell.

Questions you could ask

  • What time of day should I have my cortisol drawn?
  • Should follow-up tests use the same lab and method?
  • Could my birth control, hormone therapy or a steroid medicine have affected this result?
  • Was my blood drawn at a time of day that fits this range?
  • Should we repeat it or try a different type of cortisol test, such as saliva or a 24-hour urine collection?
  • Could a steroid medicine I take or recently stopped explain this result?

Questions people ask

Why does my report show a morning range and an afternoon range?

Cortisol follows a daily rhythm. It peaks soon after you wake, is roughly half as high by late afternoon, and is lowest around midnight. Labs print separate ranges for morning and late-afternoon samples, so the time you were drawn matters.

Does a result outside the range mean something is wrong?

Not on its own. Ranges describe most healthy people at a certain time of day. Stress, sleep, illness, birth control pills and steroid medicines can all move the number. Clinicians usually repeat the test or add others, such as ACTH, before drawing conclusions.

Why can birth control or pregnancy raise my cortisol?

Estrogen makes the liver produce more of the protein that carries cortisol in the blood. That raises total cortisol, but not necessarily the active, unbound part. Let your clinician know about any estrogen so the result is read with it in mind.

How is blood cortisol different from saliva or urine cortisol?

A blood test measures total cortisol (bound plus free) at one moment. Saliva and 24-hour urine tests mostly reflect the free, active form. Mayo notes that a 24-hour urine test or a late-night saliva test is usually preferred when Cushing syndrome is a question. Ask your clinician which fits your situation.

How do I convert µg/dL to nmol/L?

Multiply µg/dL by 27.6, so 10 µg/dL is about 276 nmol/L. To go the other way, multiply nmol/L by 0.0362.

Show the science and sources

Units

  • 1 µg/dL = 1 µg/dL
  • 1 µg/dL = 27.59 nmol/L
  • 1 µg/dL = 10 ng/mL

Open the Cortisol unit converter

Is a change real?

Cortisol naturally varies about 15.5% from test to test in the same healthy person. Between two results from the same lab, a rise of 55% or more, or a fall of 36% or more, is unlikely to be day-to-day noise or lab variation (95% reference change value). Source: The European Biological Variation Study (EuBIVAS): a summary report.

For clinicians and researchers

Cortisol is the main human glucocorticoid. Most circulating cortisol is bound to corticosteroid-binding globulin (CBG) and albumin, and under 5% is free (Mayo). Estrogen (oral contraceptives, hormone therapy, pregnancy) raises CBG and total cortisol without changing free cortisol, so free cortisol in serum, saliva or urine is preferred in those settings. Immunoassays cross-react with prednisolone (Mayo reports 41% for its Beckman Access assay), and Labcorp's Roche assay notes falsely raised results from cross-reacting steroids, including 21-deoxycortisol in 21-hydroxylase deficiency and 11-deoxycortisol during metyrapone testing. LC-MS/MS avoids most of this, and Mayo suggests it when an immunoassay result doesn't fit the clinical picture. Reference intervals depend on method and draw time. For adults, published morning intervals have lower limits of about 4.0–7 µg/dL and upper limits of about 18.4–25 µg/dL, and afternoon intervals have lower limits of about 1.8–3.0 and upper limits of about 10.5–17 µg/dL, across Labcorp, Quest, ARUP and Mayo. Mayo suggests further testing (basal ACTH, then a short cosyntropin test) when symptoms of glucocorticoid deficiency are present and the 8 a.m. cortisol is under 10 µg/dL. The 2016 Endocrine Society guideline on primary adrenal insufficiency favors the 250 µg corticotropin stimulation test (a 30- or 60-minute peak under 500 nmol/L [18 µg/dL], assay dependent, indicates insufficiency) and suggests a morning cortisol under 140 nmol/L (5 µg/dL) with ACTH only as a preliminary test when stimulation testing isn't feasible. Mayo names 24-hour urinary free cortisol (LC-MS/MS) as the preferred screen for Cushing syndrome, and its CINP page also lists midnight salivary cortisol, rather than a single serum cortisol. Use the same method for serial monitoring.

LOINC 2143-6 (primary), 14675-3, 9813-7, 9812-9, 83088-5. Specimen: serum-or-plasma.

Sources

  1. Cortisol (test 004051), Labcorp
  2. Cortisol, A.M. (test code 4212), Quest Diagnostics
  3. Cortisol, P.M. (test code 4213), Quest Diagnostics
  4. CORT: Cortisol, Serum, Mayo Clinic Laboratories
  5. CINP: Cortisol, Mass Spectrometry, Serum, Mayo Clinic Laboratories
  6. Cortisol, Serum (ARUP test 0070030), ARUP Laboratories
  7. Cortisol by LC-MS/MS, Serum or Plasma (ARUP test 2003250), ARUP Laboratories
  8. Diagnosis and Treatment of Primary Adrenal Insufficiency: An Endocrine Society Clinical Practice Guideline, Journal of Clinical Endocrinology & Metabolism (2016)
  9. Cortisol Test, MedlinePlus (NIH)
  10. Cortisol (PubChem CID 5754), PubChem (NIH)

AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.

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