Cortisol (Morning Serum Cortisol)

What is cortisol?

Cortisol is a steroid hormone — specifically a glucocorticoid — produced and secreted by the adrenal cortex, the outer layer of the adrenal glands that sit above each kidney. It is often called the "stress hormone" because it is released in large amounts during physical or psychological stress, preparing the body to respond with increased energy, heightened alertness, and suppression of non-essential processes such as digestion and reproduction.

Beyond its role in the acute stress response, cortisol performs essential functions every day: regulating blood sugar (by stimulating glucose production in the liver), modulating the immune and inflammatory response, maintaining blood pressure, and influencing mood, memory, and sleep. Its production is controlled by a hormonal cascade: the hypothalamus releases CRH, which stimulates the pituitary to release ACTH, which in turn drives the adrenal glands to produce cortisol.

Cortisol follows a strong diurnal (daily) rhythm — peaking sharply in the first hour after waking (the cortisol awakening response) and declining steadily throughout the day to its lowest point around midnight. This rhythm is why the standard blood test is performed between 8am and 9am, when levels are at their predictable peak and most informative for diagnosing adrenal disorders.

Normal cortisol range (morning)

The standard reference range for a 9am morning cortisol is:

• Normal (9am): 170–540 nmol/L
• Results below 100 nmol/L are likely insufficient and require further investigation
• Results between 100–170 nmol/L may be borderline — dynamic testing (short Synacthen stimulation test) is typically required
• Afternoon and evening cortisol values are normally much lower and cannot be interpreted against the same reference range

What a high cortisol level may indicate

A cortisol level significantly above the reference range may indicate chronic cortisol excess. Context matters greatly — acute stress, pain, and anxiety on the morning of the blood test can all temporarily elevate cortisol into or above the upper reference range. Possible clinical causes of persistently raised cortisol include:

• Cushing's syndrome — chronic excess cortisol from any source; symptoms include central weight gain, rounded face, easy bruising, stretch marks, and muscle weakness
• Cushing's disease — a pituitary tumour secreting excess ACTH, driving the adrenals to over-produce cortisol (the most common cause of Cushing's syndrome)
• Adrenal tumour — an adrenal adenoma or carcinoma autonomously producing cortisol independent of ACTH control
• Ectopic ACTH secretion — certain tumours (e.g. small cell lung cancer) produce ACTH, driving cortisol production
• Physiological stress / acute illness — cortisol is reliably raised by pain, anxiety, infection, or trauma on the day of testing

What a low cortisol level may indicate

A morning cortisol below the normal range may indicate the adrenal glands are failing to produce sufficient cortisol — a condition called adrenal insufficiency. Causes include:

• Addison's disease (primary adrenal insufficiency) — autoimmune destruction of the adrenal cortex; the most common cause in the UK; can cause fatigue, salt craving, low blood pressure, skin darkening, and weight loss
• Long-term steroid medication (secondary suppression) — regular use of oral or high-dose inhaled corticosteroids suppresses the pituitary-adrenal axis; stopping steroids abruptly can cause an adrenal crisis
• Pituitary disease (secondary adrenal insufficiency) — pituitary tumour, surgery, or radiation reducing ACTH output and thereby cortisol production
• Hypothalamic disease (tertiary adrenal insufficiency) — failure of CRH secretion from the hypothalamus
• Adrenal haemorrhage or infarction — rare but serious; can follow severe sepsis (Waterhouse-Friderichsen syndrome)

Get your cortisol tested at The Vesey

Morning cortisol testing is available at The Vesey Private Hospital, Sutton Coldfield. Appointments must be at 8–9am to capture the diurnal cortisol peak.

• Adrenal & Cortisol Profile — morning serum cortisol with clinical context review
• Advanced Hormonal Panels — cortisol included alongside other hormonal and metabolic markers

Arrive between 8am and 9am. Avoid intense exercise immediately before the test. Results reviewed by a clinician before release.

Frequently asked questions

Further reading: Cortisol — Lab Tests Online UK · Independent patient information from the British Society for Clinical Biochemistry.