Free cortisol

Cortisol is a steroid hormone, produced by the adrenal gland, which is essential for survival. Cortisol is a steroid hormone that breaks down fat and protein and stimulates glucose production in the liver. It helps the body react to physical and emotional stress, helps to regulate blood pressure, to control inflammation, and can affect cardiovascular function. The production and secretion of cortisol is stimulated by adrenocorticotrophic hormone (ACTH) produced by the pituitary gland – a tiny organ located inside the head below the brain. The concentration of cortisol in the blood increases during times of stress, and it also helps regulate the immune system. Heat, cold, infection, trauma, exercise, obesity, and debilitating disease influence cortisol secretion. The hormone is secreted in a daily pattern (circadian rhythm), rising in the early morning, through several pulses peaking around 8 a.m.(nocturnal pattern), and declining in the day to lowest concentrations in the evening (diurnal rhythm). The circadian rhythm, can change in long term night shift workers.

Inadequate concentrations of cortisol within the blood can cause nonspecific symptoms such as weight loss, muscle weakness, fatigue, low blood pressure or abdominal pain and exposure to stress can cause an adrenal crisis that requires immediate medical attention.

Decreased cortisol production may be seen as a result of:

• An underactive pituitary gland or a pituitary gland tumour that prevents ACTH production. This is known as secondary adrenal insufficiency.
• Underactive or damaged adrenal glands (adrenal insufficiency) that limit cortisol production. This is referred to as primary adrenal insufficiency and is also known as Addison’s disease.

Too much cortisol within the bloodstream can cause increased blood pressure, high blood sugar (glucose) concentrations, obesity, fragile skin, purple streaks on the tummy and muscle weakness. Women may have irregular menstrual periods and increased hair on the face; children may have delayed development and a short stature.

Increased cortisol production may be seen as a result of:

• ACTH-producing tumours, in the pituitary gland (Cushings disease) and/or in other parts of the body that stimulate the adrenal glands to produce cortisol (Cushings syndrome)
• Adrenal gland tumour or due to excessive growth of adrenal tissues (hyperplasia)

How is the sample collected for testing?

Typically, a blood sample will be taken by a syringe with needle from a vein in the arm, but sometimes urine or saliva may be tested.

Blood should ideally be collected between 8-9am when blood cortisol concentrations should be near their nocturnal peak. A second sample may be taken late in the evening when cortisol should be at its lowest concentration (about midnight). Samples collected at these times allow the doctor to evaluate the daily pattern of cortisol secretion (the diurnal variation). This pattern may be disrupted with excess cortisol production – the maximum amount may still be at or near normal concentrations, but concentrations may not fall as they should throughout the day. A single morning sample may be sufficient to detect decreased concentrations of cortisol.

Sometimes urine is tested for cortisol (urinary free cortisol); this requires collecting all urine produced during a day (24-hour urine). This sample will reflect the total amount of cortisol produced in the 24 hour period but will not allow doctors to evaluate variations in the pattern of cortisol secretion.

If a saliva sample is required for testing, the sample will be collected by inserting a swab into the mouth and waiting a few minutes while the swab becomes saturated with saliva. Your doctor may have different methods for saliva collection. Please follow any instructions that you are given.

Is any test preparation needed to ensure the quality of the sample?

Some preparation for the test may be needed. Follow any instructions that are given as far as timing of the sample collection, resting, and/or any other specific pre-test preparation.

A saliva test requires special care in obtaining the sample. You may be instructed to refrain from eating, drinking or brushing your teeth for a period of time (often between 15 to 30 minutes) prior to the test. Please discuss the instructions given by your local laboratory with your doctor and ensure you follow any instructions given.

A stimulation or suppression test requires that you have a baseline blood sample taken and are then given a specified amount of a drug. Subsequent blood samples are drawn at specific times. Please follow any instructions that you are given.