What your cortisol level means

Lab marker guide · Updated June 2026

Understanding lab results

What cortisol measures

Cortisol is a hormone made by your adrenal glands (on top of the kidneys), controlled by a signal chain from the brain — the HPA axis (hypothalamus → pituitary → adrenal). It does far more than "stress": it helps regulate blood sugar, blood pressure, metabolism, inflammation, and the sleep-wake cycle. A blood test measures the total cortisol circulating at that moment.

The daily rhythm — why timing is everything

Cortisol isn't steady through the day. It peaks in the early morning (gearing you up to wake) and falls to its lowest around midnight. That daily curve is why a single number means little on its own:

• A morning sample is the standard for screening.
• An evening or midnight value is sometimes used to look for conditions where the normal night-time dip is lost.

Your report should note the time of the draw — without it, the number can't be read properly.

Typical ranges

Cortisol is reported in µg/dL (US) or nmol/L (most of the world). Rough morning (≈8 a.m.) serum values:

Ranges vary widely by lab and assay — always read against your report.

What high cortisol means

Persistently elevated cortisol can point to Cushing's syndrome (from a tumor or long-term steroid use), but levels also rise with acute stress, illness, intense exercise, pregnancy, and certain medications. Symptoms of true excess can include weight gain around the middle, easy bruising, high blood pressure, and high blood sugar. Because so many everyday things raise it, a single high value is a prompt for follow-up testing, not a diagnosis.

What low cortisol means

A low cortisol — especially a low morning value — can signal adrenal insufficiency (Addison's disease) or a pituitary problem upstream. Symptoms can include persistent fatigue, low blood pressure, unintended weight loss, and salt cravings. Low cortisol is evaluated with confirmatory tests like an ACTH stimulation test.

Why context and trend matter

Cortisol swings with sleep, stress, and the time of day, so one reading is a snapshot of a moving target. Interpreting it well means pairing the value with when it was taken and, often, repeat or paired tests — and seeing it next to your sleep, stress, and other markers over time gives context a single PDF can't. See how to read your blood test results and tracking lab results over time.

When to talk to a doctor

Cortisol outside your lab's range for the time of day — or symptoms suggesting too much or too little — should be reviewed by a clinician, who may order timed samples or stimulation/suppression tests to find the cause. For more on understanding your panels, browse the rest of the Quanome blog.

Frequently asked questions

What is a normal cortisol level?

Because cortisol follows a daily rhythm, the range depends on when blood is drawn. A typical morning (around 8 a.m.) serum cortisol is roughly 6–23 µg/dL (about 170–635 nmol/L), falling to roughly half that by late afternoon and lowest around midnight. Labs and assays vary, so read against your report and the time it was taken.

What does high cortisol mean?

Persistently high cortisol can point to Cushing's syndrome, but it also rises with acute stress, illness, intense exercise, pregnancy, and some medications (like steroids or estrogen). One high reading isn't a diagnosis — the pattern and timing matter.

What does low cortisol mean?

Low cortisol — especially a low morning value — can indicate adrenal insufficiency (Addison's disease) or a problem with the pituitary signal. Symptoms can include fatigue, low blood pressure, weight loss, and salt cravings, and it warrants proper evaluation.

Why does the time of the cortisol test matter?

Cortisol peaks in the early morning and bottoms out at night (the diurnal rhythm). A value is only meaningful against the time it was drawn — which is why labs note the collection time and clinicians often order a morning sample or paired AM/PM tests.