What can a cortisol test tell you?
A serum cortisol test helps evaluate how well your adrenal glands are functioning and whether your body is producing too much or too little cortisol.
Low cortisol levels can be a sign of Addison’s disease or other forms of adrenal insufficiency, in which the adrenal glands do not make enough cortisol. Low blood sugar can also cause cortisol to spike, so in some cases, a cortisol test may illuminate hypoglycemia.
Because cortisol production is closely regulated by adrenocorticotropic hormone (ACTH) from the pituitary gland, providers often order ACTH tests alongside cortisol to identify whether the problem originates in the adrenal glands or elsewhere in the hormonal chain.
Cortisol tests can also point to stress-related conditions, including post-traumatic stress disorder (PTSD) or chronic stress.
The Endocrine Society typically recommends cortisol testing when symptoms suggest adrenal dysfunction or when an adrenal or pituitary disorder is suspected.
What is being tested?
Cortisol is a hormone produced by the adrenal cortex (the outer layer of the adrenal glands). It helps regulate metabolism, suppress inflammation (in the short-term), and control your body’s stress response.
When you’re under stress — whether physical (like infection or surgery) or emotional — the hypothalamus signals the pituitary gland to release ACTH, which stimulates the adrenal glands to release cortisol. Once the stress resolves, cortisol levels drop through a negative feedback system.
Testing serum cortisol helps providers assess this hormonal loop and identify whether your adrenal glands are overactive or underactive.
Where is the cortisol test typically included?
A cortisol test can be ordered as a stand-alone blood test or as part of a hormonal evaluation panel. It may be included in:
Endocrine function panels (to assess adrenal and pituitary hormones).
Dynamic tests such as:
ACTH stimulation test, which evaluates the adrenal response to synthetic ACTH.
Dexamethasone suppression test, which helps determine if the body is producing too much cortisol.
For context, cortisol can also be measured in saliva or urine.
Salivary cortisol reflects the free (biologically active) form of the hormone and is often used to check for abnormal daily cortisol rhythms.
Urinary free cortisol (24-hour urine test) measures total cortisol output over a full day and can help confirm suspected Cushing’s syndrome.
However, serum cortisol remains the standard for initial adrenal evaluation and is most commonly used in general clinical settings.
Who should get a cortisol test?
A cortisol blood test may be recommended if you have symptoms or conditions that point to adrenal or pituitary dysfunction.
Common reasons for testing:
Unexplained weight gain or loss.
Fatigue or weakness that doesn’t improve with rest.
Unusually low blood pressure or fainting spells.
New or worsening depression, anxiety, or irritability.
Irregular menstrual cycles or loss of libido.
Persistent high blood pressure not explained by other causes.
Risk factors and conditions that may warrant testing:
Long-term corticosteroid use.
Pituitary or adrenal tumors.
Chronic stress or prolonged illness.
Autoimmune conditions affecting hormone production.
Family history of endocrine disorders.
Your provider may recommend testing both cortisol and ACTH to understand whether an issue stems from the adrenal glands or from the pituitary’s signaling to those glands.
