What Is Cortisol in a Blood Test?

Q: What Is Cortisol in a Blood Test?

Cortisol testing explained: normal morning range 6-23 µg/dL, why timing matters, what high cortisol (Cushing's) and low cortisol (Addison's) mean.

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

Source: NLM MedlinePlus, American Association for Clinical Chemistry.

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