The Cortisol (Serum – 8 AM) test is a blood test that measures the level of cortisol in your bloodstream in the morning, typically around 8 AM. Cortisol is often called the “stress hormone,” but it does much more than respond to stress. It is made by the adrenal glands (small glands that sit on top of the kidneys) and helps regulate blood pressure, blood sugar, metabolism, immune response, and how your body reacts to illness or injury.

Cortisol follows a normal daily rhythm (a “diurnal” pattern): it is usually highest in the early morning and gradually decreases throughout the day, reaching its lowest levels near midnight. That is why measuring cortisol at 8 AM is especially useful—this timing captures the expected peak and helps clinicians interpret whether the adrenal glands are producing an appropriate amount.

In plain language, the results generally mean:

Low morning cortisol may suggest that your body is not making enough cortisol. This can happen with adrenal insufficiency, including Addison’s disease, or when the pituitary gland does not signal the adrenals properly. Low cortisol can also occur after long-term use of steroid medications (like prednisone), because these can temporarily “turn down” your body’s natural cortisol production.

High morning cortisol may suggest that your body is making too much cortisol. This can happen with Cushing’s syndrome (excess cortisol production), prolonged severe stress or illness, or as a side effect of taking steroid medications. Because cortisol rises with physical or emotional stress, one elevated value does not always confirm disease—your clinician may use additional testing to confirm the cause.

This test is often interpreted alongside symptoms, medical history, medications (including inhaled, topical, oral, or injected steroids), and sometimes other hormone tests such as ACTH or follow-up dynamic testing (for example, an ACTH stimulation test) if needed.

Doctors commonly order an 8 AM serum cortisol test to evaluate symptoms that may point to problems with the adrenal glands or the hormone pathways that control them. It may be used to help screen for or support evaluation of Addison’s disease, adrenal insufficiency, or Cushing’s syndrome.

This test may be recommended if you have symptoms of low cortisol (possible adrenal insufficiency), such as:

Unusual or persistent fatigue, weakness, dizziness (especially when standing), low blood pressure, unexplained weight loss, decreased appetite, nausea/vomiting, abdominal pain, salt cravings, low blood sugar symptoms, or skin darkening (hyperpigmentation) in some cases.

It may also be ordered if you have symptoms of high cortisol (possible Cushing’s syndrome), such as:

Unexplained weight gain (especially around the abdomen and face), a rounded “moon face,” easy bruising, purple stretch marks, muscle weakness, thinning skin, acne, high blood pressure, elevated blood sugar/diabetes, mood changes, sleep disturbance, or bone loss.

Other common reasons include:

Monitoring or evaluating possible adrenal suppression after long-term corticosteroid therapy (such as prednisone, dexamethasone, hydrocortisone), assessing adrenal function in people with pituitary disorders, or investigating abnormal electrolyte patterns (such as low sodium) when adrenal issues are suspected.

Because cortisol changes throughout the day and can be affected by stress, illness, shift work, pregnancy, and certain medications, your clinician may give specific instructions about timing and may recommend additional tests to confirm a diagnosis.

• Addison’s disease (primary adrenal insufficiency)
• Adrenal insufficiency (primary or secondary)
• Cushing’s syndrome (hypercortisolism)
• Pituitary disorders affecting ACTH (e.g., ACTH deficiency; ACTH-secreting pituitary adenoma/Cushing disease)
• Adrenal tumors (cortisol-producing adenoma or carcinoma)
• Adrenal suppression due to long-term corticosteroid use

• Assessing adrenal health and cortisol production patterns
• Screening for or monitoring suspected Cushing’s syndrome or Addison’s disease
• Supporting evaluation of chronic fatigue, weakness, unexplained weight changes, or persistent dizziness
• Helping guide safe tapering and recovery after prolonged steroid medication use
• Clarifying possible hormone-related contributors to high blood pressure or abnormal blood sugar
• Overall endocrine (hormone) assessment when symptoms suggest pituitary–adrenal imbalance