According to the National Institutes of Health (NIH), cortisol levels vary throughout the day. Cortisol peaks in the morning, and normal blood cortisol levels at 8 in the morning usually range from 6 to 23 micrograms per deciliter. Different laboratories may use different ranges.
According to the NIH, cortisol is a hormone produced by the adrenal glands that helps the body to handle physical and emotional stress. Because cortisol cycles throughout the day, a urine collection taken over 24 hours may give a better idea of cortisol levels than a single blood test. The normal range for this test is usually 10 to 100 micrograms per 24 hours. Too much cortisol in the blood or urine may indicate Cushing's syndrome, while too little may indicate Addison's disease.