Lab test glossary · Hormones
Cortisol: what it means
Also known as: serum cortisol, AM cortisol
Cortisol is your body's main stress hormone, and it follows a strong daily rhythm — which is why the time of the draw is everything.
What it measures
Cortisol, made by the adrenal glands, helps regulate metabolism, blood sugar, blood pressure, and the stress response. It follows a daily curve — highest in the early morning, lowest at night — so a cortisol value only means something when you know what time it was drawn. Abnormal results are usually followed up with more specific testing.
Typical range
A morning (around 8 a.m.) level is often roughly 6–23 µg/dL, but interpretation depends entirely on timing and the reason for testing.
Reference ranges differ between labs and are printed on your own report — always read your result against that range, not a general one.
What a high result can mean
- Physical or emotional stress and illness
- Steroid medications
- Cushing's syndrome (uncommon)
A high value is a starting point for a conversation, not a diagnosis — many causes are benign or temporary.
What a low result can mean
- Adrenal insufficiency (uncommon but important)
- Having recently stopped steroid medication
Why the trend matters
Because cortisol swings across the day, single values are noisy — clinicians rely on properly-timed tests and patterns rather than one reading.
When to talk to your doctor
Discuss cortisol testing and any clearly abnormal result with your doctor, who will interpret it with timing and symptoms in mind.
Frequently asked questions
What time should cortisol be tested?
Cortisol is highest in the early morning and lowest at night, so a value only means something when the draw time is known — morning (around 8 a.m.) testing is standard.
Can stress raise cortisol on a blood test?
Yes — physical and emotional stress and illness raise cortisol, which is one reason an isolated high value often isn't meaningful on its own and is usually followed up with more specific testing.
What are symptoms of high cortisol?
Persistently high cortisol can be associated with weight gain, high blood pressure, and other changes — but everyday stress raises cortisol temporarily too, so timed testing and clinical context matter far more than a single value.
This page is general education about a common lab test — it isn’t medical advice and can’t interpret your specific result. What a value means depends on your history, symptoms, and the rest of your labs, which is a conversation for you and your clinician.