Free cortisol vs total cortisol: what each test measures

Free cortisol is the part of your cortisol that isn’t attached to a protein. Total cortisol is that free part plus everything that is attached. A standard blood test reports total cortisol, while urine and saliva tests reflect the free part. The two answer slightly different questions.

This page explains the difference, which tests measure which, when it matters and what to ask for. It is general information and not a way to read your own result.

Cortisol

One blood draw for one cortisol result. It can’t diagnose or rule out an adrenal condition by itself.

$109

The seller's page for this test doesn't say whether it reports total or free cortisol. Check before you order. Free cortisol is usually measured in urine or saliva, which are different tests.

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Price checked November 2026. Not available in ND, RI, NY, NJ, MD and HI. We earn a commission on sales.

Free and total cortisol in plain terms

Cortisol is carried in the blood on proteins. A 2024 review in Endocrine Reviews puts it this way: roughly 90% of serum cortisol is bound to CBG, 4% to 6% is bound to other proteins such as albumin, and 4% to 6% circulates freely. It says binding to CBG is a major determinant of bioavailability.

• Total cortisol is all of it: bound and free. This is what an ordinary blood (serum or plasma) cortisol test reports. A review in the International Journal of Molecular Sciences notes that blood sampling measures total cortisol, and that only the free fraction is biologically active.
• Free cortisol is the unbound part. Only free cortisol is filtered into urine and saliva, so a urine or saliva test gives a direct view of it (Diagnostics, 2023).

When the difference matters

Anything that changes how much carrier protein there is changes total cortisol, even when free cortisol hasn’t moved.

Situation	Effect on total cortisol	What the sources add
Oral estrogen, including some birth control pills	Higher, from more CBG	Urine and saliva tests are not affected by changes in CBG
Pregnancy	Higher, from more CBG	Urine free cortisol also rises normally later in pregnancy, up to 3-fold by term in one review
Nephrotic syndrome (a kidney condition)	Lower, from loss of CBG	Can lead to a false diagnosis of adrenal insufficiency after a stimulation test
Low albumin, as in critical illness	Lower	Free cortisol was similar in the study cited below

In the albumin example, the Endocrine Reviews paper reports total cortisol of 435 against 633 nmol/L in people with and without low albumin, but free cortisol of 140 against 143 nmol/L. It says oral estrogens, and the high estrogen levels of pregnancy, give a falsely elevated total cortisol.

That is why the review says measuring free cortisol was proposed to have better clinical use in people whose total cortisol is near a diagnostic threshold, or who have altered binding proteins. Our page on CBG goes into the carrier protein itself.

How free cortisol is measured

There are three routes.

1. 24-hour urine. The free cortisol that passes into urine over a day is added up. This is the 24-hour urinary free cortisol test.
2. Saliva. Free cortisol passes into saliva, and a change in blood levels is reflected quickly. A late-night saliva sample checks whether cortisol drops at night.
3. Free cortisol in blood. The lab removes the bound fraction by ultrafiltration, equilibrium dialysis or gel-filtration chromatography. The Endocrine Reviews paper calls these techniques labor-intensive and slow. Free cortisol can also be estimated with an equation, but those estimates can be inaccurate when albumin or CBG is abnormal. The 2023 laboratory review says free hormone analysis in blood is not widely available and not superior to salivary analysis.

MedlinePlus says measuring cortisol in urine and saliva is an accurate way to estimate how much is in your blood. See the saliva, urine and hair page for what each collection involves.

The 24-hour urine free cortisol test

You collect all urine for 24 hours. MedlinePlus says the steps are to urinate in the toilet and note the time, then collect all urine for the next 24 hours in the container you are given, kept in a refrigerator or a cooler with ice, and to return it as instructed. NIDDK says higher than normal levels suggest Cushing’s syndrome.

Points to know:

• Two collections are recommended, because day-to-day variation is high (2026 review).
• Collection errors matter. An incomplete collection is a risk, so labs may also check urine creatinine and volume.
• Kidney function matters. The 2026 review says saliva is preferred over urine when creatinine clearance is below 60 mL/min or urine volume exceeds 5 L in 24 hours. The 2023 laboratory review also says very high fluid intake can raise the result.
• It is less sensitive for mild cases, and a mild but steady rise in total cortisol can give a normal urine result.

A frequent question is what the normal range for urinary free cortisol is. The sources used for this site don’t give one figure to rely on. The 2023 laboratory review says immunoassays can over-measure urinary cortisol, and so cut-offs have to be specific to the method. Use the reference range printed on your own report and go over it with a clinician.

What “LC-MS/MS” means on a free cortisol order

You may see “cortisol, free, LC/MS/MS” on an order. LC-MS/MS stands for liquid chromatography with tandem mass spectrometry. It identifies the cortisol molecule itself instead of relying on antibodies. A review for general practitioners says it is the most validated method for measuring free cortisol in saliva and urine, because immunoassays tend to give false-positive results. Immunoassays can also react with similar steroids, such as prednisolone. LC-MS/MS is not available everywhere.

Which one should you ask for?

Your question	What usually fits	Why
Is my morning cortisol low?	Total serum cortisol, often with ACTH	The standard first step for suspected adrenal insufficiency. See testing for low cortisol.
Could I have Cushing’s syndrome?	24-hour urine free cortisol, late-night saliva test or a dexamethasone suppression test	Free-cortisol tests aren’t thrown off by carrier proteins. See testing for high cortisol.
I take oral estrogen or am pregnant	Tell the clinician before any cortisol test	Total cortisol can read high without the free part being high.
I just want a number to bring to a clinician	A total serum cortisol	It is the common, widely available blood test.

Which test fits is a clinician’s decision. Don’t stop a medicine, including oral estrogen or a steroid, to prepare for a test. Ask the prescriber.

What the seller’s cortisol test reports

The seller’s page for its single cortisol test refers to “serum cortisol levels” and doesn’t say whether it measures total or free cortisol. A blood draw is usually reported as total cortisol, but the seller’s page doesn’t confirm that, so check before you order if the difference matters for your question. The page also states no fasting rule and no draw time, so follow the instructions on your lab order. The seller’s own page adds that a single value is hard to interpret.

A single total cortisol can’t diagnose or rule out Cushing’s syndrome or adrenal insufficiency, whichever form it is. See the cortisol test guide for the whole picture and the test finder to compare options.

Questions people ask

Is free cortisol better than total cortisol?

Not as a rule. It answers a different question. Free cortisol has been proposed as more useful when carrier proteins are altered or a total value is near a threshold. Total cortisol is the standard blood measurement and is what published blood ranges describe. The 2023 laboratory review says free cortisol in blood is not widely available.

What is a normal total cortisol level?

It depends on the time of day and the lab. One review gives 3 to 23 µg/dL for total serum cortisol at 8 a.m. and 3 to 13 µg/dL at 4 p.m. Another source lists slightly different morning and afternoon ranges. Labs print their own. The normal range page shows both and where they come from, and the units converter helps if your report is in nmol/L.

Do saliva tests measure free cortisol?

Yes. Only free cortisol passes into saliva. A 2024 review reports that salivary cortisol and cortisone correlated well with serum free cortisol.