Cortisol

Cortisol is a hormone produced by the adrenal glands. 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 has a range of roles in the body. It helps break down protein, glucose, and lipids, maintain blood pressure, and regulate the immune system. Heat, cold, infection, trauma, stress, exercise, obesity, and debilitating disease can influence cortisol concentrations. The hormone is secreted in a daily pattern, rising in the early morning, peaking around 8 am, and declining in the evening. This pattern, which is sometimes called the "diurnal variation" or "circadian rhythm," changes if you work irregular shifts (such as the night shift) and sleep at different times of the day.

Inadequate amounts of cortisol can cause nonspecific symptoms such as weight loss, muscle weakness, fatigue, low blood pressure, and abdominal pain. Sometimes decreased production combined with a stressor 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 abdomen, muscle weakness, and osteoporosis. Women may have irregular menstrual periods and increased facial hair; children may have delayed development and a short stature.

Typically, blood will be drawn from a vein in the arm, but sometimes urine or saliva may be tested. Cortisol blood tests may be drawn at about 8 am, when cortisol should be at its peak, and again at about 4 pm, when the level should have dropped. Sometimes a resting sample will be obtained late in the evening to measure cortisol when it should be at its lowest concentration in the blood (about midnight). Obtaining more than one sample allows 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 usually requires collecting all the urine produced during a day and night (a 24-hour urine), but sometimes may be done on a single sample of urine collected in the morning. A 24-hour urine sample may be ordered to measure the amount of free (not protein bound) cortisol. This sample will show the total amount of unbound cortisol secreted in the urine but it will not allow doctors to evaluate variations in cortisol secretion.

Cortisol testing of saliva can be performed. Although the sampling is less stressful than a blood draw, it requires special care in obtaining the sample. Often, the sample is collected between 11 pm and midnight, the time when cortisol is normally at its lowest, to help diagnose Cushing's syndrome.

No test preparation is needed.