What is being tested?
Cortisol is a steroid hormone, produced by the adrenal gland, which is essential for survival. Production and secretion of cortisol is stimulated by ACTH (adrenocorticotropic hormone), a hormone produced by the pituitary gland – a tiny organ located inside the head below the brain. Cortisol levels increases in times of stress, and also help regulate the immune system. Heat, cold, infection, trauma, exercise, obesity, and debilitating disease influence cortisol secretion. The hormone is secreted in a daily pattern, rising in the early morning, peaking around 8 a.m., and declining in the evening. This pattern, a “diurnal variation” or “circadian rhythm,” can change in long term night shift workers.

Inadequate amounts of cortisol 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.

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

How is the sample collected for testing?
Typically, blood will be taken from a vein in the arm, but sometimes urine may be tested. Cortisol blood tests may be taken at about 8 am, when blood cortisol concentrations should be at their peak, and a second sample may be taken late in the evening when cortisol should be at its lowest concentration in the blood (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 be at or near normal concentrations, but levels 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; 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 cortisol secretion.