Cortisol test explained

Cortisol is a hormone made by the adrenal cortex and belongs to the group of glucocorticoids. It helps the body respond to stress and regulates the metabolism of glucose, protein and fat, blood pressure and the working of the immune system. Cortisol production is controlled by ACTH (adrenocorticotropic hormone), which is made by the pituitary gland and in turn depends on signals from the hypothalamus — this chain is called the hypothalamic-pituitary-adrenal axis. The amount of cortisol in the blood is not constant: it is highest in the morning shortly after waking and lowest late in the evening — this variation is set by the daily rhythm (the cortisol curve). That is why a cortisol blood test is most often done in the morning, at about 8 o'clock, and is sometimes repeated in the evening as well, to assess whether the daily rhythm remains normal. The test is used when a disorder of the adrenal glands or of the pituitary gland is suspected — both too much and too little production of the hormone.

• When Cushing's syndrome is suspected — when there is rapid weight gain, a moon-shaped face, purple stretch marks on the skin, easy bruising, muscle weakness
• When Addison's disease or adrenal insufficiency is suspected — when there is persistent tiredness, muscle weakness, loss of appetite and weight, abdominal pain
• When assessing pituitary function, when ACTH production is thought to be impaired
• When a doctor wants to check the working of the adrenal glands or the pituitary gland after a head injury or surgery
• When monitoring treatment, where a cortisol disorder has been found previously

A raised cortisol is, according to MedlinePlus, considered a possible sign of Cushing's syndrome — it can be caused by a pituitary or an adrenal tumour, and also by severe stress or an acute illness. The typical signs are weight gain, a moon-shaped face, easy bruising and muscle weakness.

• Cushing's syndrome — a pituitary or adrenal tumour producing too much of the hormone
• Ectopic Cushing's syndrome — an ACTH-producing tumour elsewhere in the body
• An adrenal tumour
• Severe stress or an acute illness

Symptoms that can accompany a raised cortisol

• Weight gain, especially around the waist, with thinner arms and legs
• A moon-shaped face
• An increased amount of fat around the neck and shoulders
• Easy bruising
• Purple stretch marks on the skin
• Muscle weakness

What to discuss with a doctor

• Whether there was stress, an acute illness or glucocorticoid use at the time of the test — that can raise the result temporarily
• An ACTH test, which helps to separate pituitary from adrenal causes
• An imaging test of the adrenal glands or the pituitary gland, if a tumour is suspected
• When to repeat the test, so that the daily rhythm can be seen

A low cortisol, according to MedlinePlus, may indicate Addison's disease, pituitary insufficiency, or suppression after long-term use of glucocorticoids. Addison's disease is most often caused by damage to the adrenal glands due to an autoimmune condition, tuberculosis or HIV, while secondary insufficiency is associated with pituitary disorders or a head injury.

• Addison's disease — damage to the adrenal glands due to an autoimmune condition, tuberculosis or HIV
• Pituitary insufficiency (hypopituitarism) — due to a disease of the pituitary gland, a head injury or surgery
• Suppression after long-term use of glucocorticoids

Symptoms that can accompany a low cortisol

• Persistent tiredness
• Muscle weakness
• Loss of appetite and weight loss
• Abdominal pain

What is usually assessed with a low result

• An ACTH test, which helps to separate adrenal from pituitary causes
• An adrenal function stimulation test, if insufficiency is suspected
• Whether glucocorticoids are being taken or were stopped recently
• When to repeat the test, so that the change over time can be seen

Units, repeat testing and related indicators

For adults, in a blood sample taken at about 8 in the morning, MedlinePlus gives a range of 138-690 nmol/l, and in other units 5-25 mcg/dl (converted to nmol/l by ×27.59). You will find the exact interval used by your laboratory on your own result report. The amount of cortisol in the blood varies over the day, so the test is most often done in the morning, and is sometimes repeated in the evening to assess whether the daily rhythm remains normal. The result should be discussed with a doctor together with the symptoms and other tests. Related indicators: ACTH, TSH, glucose, DHEA-S, and also how to read blood test results.