What this marker measures
Cortisol has a pronounced diurnal rhythm — it is highest in the morning (around 8 AM) and lowest late at night. Results must always be interpreted relative to the time of blood draw. Dynamic tests (ACTH stimulation, dexamethasone suppression) are typically needed for diagnosis rather than a single level.
High or low: what it can mean
High Cortisol
Consistently elevated cortisol may suggest Cushing's syndrome (overproduction by adrenal glands), prolonged use of corticosteroid medications, or chronic stress. A single high result must be interpreted cautiously, as cortisol rises with acute physical stress, illness, or anxiety.
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Low Cortisol
Low cortisol can indicate adrenal insufficiency (Addison's disease) or suppression from prior corticosteroid use. Symptoms can include fatigue, low blood pressure, salt craving, and weight loss. Early morning cortisol is the most informative single measurement.
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Frequently asked questions
What is Cortisol?
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Cortisol is the body's primary stress hormone, produced by the adrenal glands. It regulates the stress response, blood sugar, immune function, anti-inflammatory processes, and metabolism.
What does Cortisol measure?
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Cortisol has a pronounced diurnal rhythm — it is highest in the morning (around 8 AM) and lowest late at night. Results must always be interpreted relative to the time of blood draw. Dynamic tests (ACTH stimulation, dexamethasone suppression) are typically needed for diagnosis rather than a single level.
What does high Cortisol mean?
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Consistently elevated cortisol may suggest Cushing's syndrome (overproduction by adrenal glands), prolonged use of corticosteroid medications, or chronic stress. A single high result must be interpreted cautiously, as cortisol rises with acute physical stress, illness, or anxiety.
What does low Cortisol mean?
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Low cortisol can indicate adrenal insufficiency (Addison's disease) or suppression from prior corticosteroid use. Symptoms can include fatigue, low blood pressure, salt craving, and weight loss. Early morning cortisol is the most informative single measurement.
Related biomarkers
Editorial note
LabTestly explains lab markers using plain-English educational content. Reference ranges may vary by laboratory and should be interpreted with a clinician.
Educational content · Editorially reviewed for clarity · Last updated
Common sources used for lab-test education
Not medical advice
This page is for general understanding only and does not replace medical advice from your clinician. Reference ranges can vary by laboratory, age, sex, pregnancy status, medications, and clinical context.