Cortisol is produced by the adrenal glands. It is an essential hormone in stress situations (disease, surgery, hypoglycemia, etc.). However, overactive adrenal glands (Cushing’s disease, etc.) are harmful to the body (suppresses the immune response, etc.). Cortisol levels vary depending on the time of day when the sample is taken: high in the early morning and low in the evening. Cortisol levels can be measured in the blood, urine or saliva. The advantage of saliva testing is the ability to take multiple samples during the day, including late in the evening when levels should be at their lowest.
High levels of salivary cortisol late in the evening are highly suggestive of Cushing’s disease and are probably the most sensitive test for milder forms of the disease. Elevated results should preferably be confirmed by additional salivary or blood tests. Acute stress, alcoholism, depression, pregnancy and several medications including estrogens can increase salivary cortisol levels. Even minimal bleeding of the gums can lead to abnormally high salivary cortisol levels, and it is extremely important to take proper sampling precautions. The test is not sensitive enough to diagnose underactive adrenal glands (Addison’s disease).