What Is a Cortisol Blood Test?

Q: What Is a Cortisol Blood Test?

Cortisol testing: normal morning 6-23 µg/dL. Timing is critical — cortisol peaks in morning, drops at night. High = Cushing's, low = Addison's.

Cortisol is the primary stress hormone. It follows a circadian rhythm.

Normal (8 AM)

6–23 µg/dL
Afternoon is roughly half

High Cortisol

Cushing's syndrome
Chronic stress
Oral steroids
Obesity

Low Cortisol

Addison's disease
Pituitary insufficiency
Steroid withdrawal

Alternative Tests

24-hour urine free cortisol
Midnight salivary cortisol
Dexamethasone suppression test

Source: Endocrine Society, NLM MedlinePlus.

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