Cortisol Levels in Blood are measured for patients who are suspected to have Hyperfunctioning or Hypofunctioning Adrenal Glands. There is an elaborate feedback mechanism for cortisol coordinates the function of the hypothalamus, pituitary gland, and adrenal glands. When Corticotropin-releasing Hormone (CRH) is produced in the hypothalamus, it stimulates the production of Adrenocorticotropic Hormone (ACTH) in the Anterior Pituitary Gland. ACTH then stimulates the Adrenal Cortex in order to produce Cortisol. The increased Cortisol Levels will be considered as a negative feedback which limits or cutoff the production of both CRH and ACTH. Cortisol is a potent glucocorticoid released from the adrenal cortex. This hormone affects the metabolism of carbohydrates, proteins, and fats. It has a profound effect on glucose serum levels. Cortisol tends to increase glucose by stimulating gluconeogenesis from glucose stores. It also inhibits the effect of insulin and thereby inhibits glucose transport into the cells.
The best method of evaluating adrenal activity is by directly measuring plasma cortisol levels. Normally cortisol levels increase and decrease during the day; this is called the Diurnal Variation. Cortisol levels are normally the highest after a long period of sleep, which is around 6 AM to 8 AM and gradually fall during the day, reaching their lowest Cortisol Level around midnight.
Abnormalities to the natural diurnal variation can be one the earliest indications of Adrenal Hyperfunction, even if before finding any indications of abnormally high cortisol levels. For example, patients who have Cushing Syndrome usually have upper normal plasma cortisol levels which normally seen in the morning. However, their Cortisol Levels don’t decrease during the day. High levels of cortisol indicate Cushing syndrome, and low levels of plasma cortisol are suggestive of Addison disease.
For this test, blood is usually collected at 8 AM and again at around 4 PM. The 4 PM value is anticipated to be one third to two thirds of the 8 AM value. Normal values may be transposed in individuals who have worked during the night and slept during the day for long periods of time.
Normal Blood Cortisol Levels
Newborn: 1-24 mcg/dL.
Children (1-16 years):
8 AM: 3-21 mcg/dL.
4 PM: 3-10 mcg/dL .
8 AM: 5-23 mcg/dL or 138-635 nmol/L (SI units)
4 PM: 3-13 mcg/dL or 83-359 nmol/L (SI units)
Causes of False Cortisol Levels
- Pregnancy is normally accompanied with increased Cortisol Levels.
- Physical and emotional stress can elevate cortisol levels. Stress stimulates the pituitary-cortical mechanism and thereby stimulates Cortisol production.
- Drugs that may cause increased levels include Amphetamines, Cortisone, Estrogen, Oral Contraceptives, and Spironolactone (Aldactone).
- Drugs that may cause decreased levels include Androgens, Aminoglutethimide, Betamethasone and other Exogenous Steroid medications, Danazol, Lithium, Levodopa, Metyrapone, and Phenytoin (Dilantin).
Causes of High Cortisol Levels
- C0ushing Syndrome (Adrenal Adenoma or Adrenal Carcinoma): The neoplasm produces cortisol without regard to the normal feedback mechanism.
- Hyperthyroidism: The metabolic rate is increased and cortisol levels rise accordingly to maintain the elevated glucose needs.
- Obesity: All sterols are increased in the obese, perhaps because fatty tissue may act as a depository or site of synthesis.
Cortisol rises when ACTH is overproduced as a result of Neoplastic overproduction of ACTH in the Pituitary or elsewhere in the body by an ACTH-producing cancer. Stress is also potent stimulus to ACTH production. ACTH overproduction that leads to High Cortisol Levels can be an indication of:
- Cushing Disease.
- Ectopic ACTH-producing Tumors.
Causes of Low Cortisol Levels
- Adrenal Hyperplasia: The congenital absence of important enzymes in the synthesis of cortisol prevents adequate serum levels.
- Addison Disease: As a result of Hypofunctioning of the Adrenal Gland, Cortisol levels drop.
- Hypopituitarism: ACTH is not produced by the pituitary gland, which is destroyed by disease, neoplasm, or ischemia. The adrenal gland is not stimulated to produce cortisol.
- Hypothyroidism: Normal cortisol levels are not required to maintain the reduced metabolic rate of hypothyroid patients.