Cortisol (serum/plasma) concentration

This test measures the level of cortisol, a hormone made by your adrenal glands, to help your doctor check how well your body is managing stress, metabolism, blood pressure, and immune function.

Your doctor may order cortisol testing to diagnose or monitor conditions like adrenal gland disorders (such as Cushing’s syndrome or Addison’s disease), evaluate symptoms of stress or fatigue, or check for hormonal imbalances. It may also be used in situations where cortisol levels fluctuate throughout the day, such as in certain sleep disorders or pituitary issues.

Before the test, your doctor may ask you to stop taking certain medicines, such as steroids or birth control pills, and to avoid strenuous exercise and stressful situations, since these can affect your cortisol levels.

No special preparation is usually needed, but your doctor might instruct you to fast for 8–12 hours before the test if cortisol is measured at a specific time (e.g., morning or evening). If you’re taking medications that affect cortisol, let your lab staff know. Avoid caffeine or alcohol before the test if advised.

During the test, a blood sample is usually drawn from a vein in your arm and takes only a few minutes. Some cortisol tests instead use a 24-hour urine collection or a saliva sample, depending on what your doctor orders.

A blood sample will be drawn from a vein in your arm by a healthcare professional. You may feel a slight pinch, but it typically doesn’t cause significant discomfort. The process takes a few minutes, and you can resume normal activities afterward.

Your results show whether your cortisol level is normal, high, or low. High levels may point to conditions such as Cushing syndrome, while low levels can suggest adrenal insufficiency, and your doctor will explain what your specific numbers mean.

Results are interpreted based on your doctor’s clinical context, including your symptoms, medical history, and timing of the sample (e.g., morning vs. evening). Abnormally high or low cortisol levels may indicate underlying health concerns that require further evaluation.