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Cortisol Blood Test: What Your Results Mean

Cortisol is the primary stress hormone produced by the adrenal glands (located above each kidney). It regulates the body's response to physical and psychological stress, controls blood sugar levels, reduces inflammation, and influences metabolism, immune function, blood pressure, and sleep-wake cycles. Cortisol follows a strong diurnal rhythm — it is highest in the early morning (peaking around 8 AM) and lowest at night, which is why timing of the blood draw matters greatly for interpretation.

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Normal Range

6 – 23 µg/dL (morning)

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Unit

µg/dL

What Your Results Mean

Normal

A normal morning cortisol level indicates that the adrenal glands are functioning properly and the hypothalamic-pituitary-adrenal (HPA) axis is regulating cortisol release appropriately. Your body has an effective stress response and the right amount of cortisol for metabolic and immune regulation.

High

Persistently high cortisol (hypercortisolaemia) may indicate Cushing's syndrome — caused by a pituitary adenoma, adrenal tumour, or long-term corticosteroid medication use. Symptoms include central weight gain (especially a "buffalo hump" and moon face), stretch marks, high blood pressure, muscle weakness, and poor wound healing. Psychological stress and depression also raise cortisol transiently.

Low

Low cortisol suggests adrenal insufficiency. Primary adrenal insufficiency (Addison's disease) occurs when the adrenal glands are damaged and cannot produce enough cortisol. Secondary adrenal insufficiency results from pituitary failure to produce ACTH. Symptoms include profound fatigue, weight loss, low blood pressure, salt craving, and nausea. Abrupt steroid withdrawal is a common preventable cause.

Frequently Asked Questions

Why does the timing of a cortisol test matter? expand_more
Cortisol follows a diurnal (circadian) rhythm — levels peak in the early morning (around 6–8 AM) and drop to their lowest at night. A morning cortisol test provides the most clinically useful reference point. An afternoon or evening test will naturally show lower levels.
What is Cushing's syndrome? expand_more
Cushing's syndrome is a condition caused by prolonged exposure to excess cortisol. It can result from a tumour in the pituitary gland (Cushing's disease), an adrenal tumour, or long-term use of corticosteroid medications. Symptoms include central obesity, moon face, purple stretch marks, and muscle weakness.
What is Addison's disease? expand_more
Addison's disease (primary adrenal insufficiency) occurs when the adrenal glands are damaged — most often by autoimmune destruction — and cannot produce adequate cortisol or aldosterone. It causes chronic fatigue, low blood pressure, salt craving, and darkening of the skin. It requires lifelong cortisol replacement therapy.
Can chronic stress cause permanently high cortisol? expand_more
Chronic psychological stress raises cortisol over time, but true clinical hypercortisolaemia (Cushing's syndrome) is a distinct medical condition usually caused by a tumour or medication. Elevated cortisol from lifestyle stress is a real concern but rarely reaches diagnostic levels for Cushing's.
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