What Is Cortisol in a Blood Test?

Cortisol is the primary stress hormone produced by your adrenal glands. It follows a circadian rhythm — highest in early morning, lowest at midnight.

Normal Range (8 AM)

• 6–23 µg/dL
• Afternoon levels are roughly half of morning
• Always record time of draw

High Cortisol Causes

• Cushing’s syndrome — pituitary tumor, adrenal tumor, ectopic ACTH
• Chronic stress
• Oral corticosteroids
• Obesity
• Depression and alcoholism — pseudo-Cushing’s

Low Cortisol Causes

• Addison’s disease — primary adrenal insufficiency
• Pituitary insufficiency — secondary
• Sudden steroid withdrawal
• Congenital adrenal hyperplasia

Alternative Testing

• 24-hour urinary free cortisol
• Midnight salivary cortisol
• Dexamethasone suppression test
• ACTH level — distinguishes primary from secondary