Cortisol (hydrocortisone/compound F) is a glucocorticosteroid of the adrenal cortex and affects metabolism of proteins, carbohydrates, and lipids. Cortisol stimulates glucogenesis by the liver, inhibits the effect of insulin, and decreases the rate of glucose use by the cells. Eighty to 90% of cortisol is carried in the blood bound to corticosteroid-binding globulin, 5%–7% bound loosely to albumin, and the remainder unbound.

In health, the secretion rate of cortisol follows a diurnal pattern, being higher in the early morning (6:00–8:00 a.m.) and lower in the evening (4:00–6:00 p.m.). This variation is lost in patients with Cushing syndrome and in persons under stress.

The cortisol test evaluates adrenal hormone function. Suppression and stimulation tests may also be done. Dexamethasone suppression test (DST) screens for Cushing syndrome and identifies depressed persons who are likely to respond to antidepressants or electroshock therapy. It is based on the fact that ACTH production is suppressed in healthy persons after a low dose of dexamethasone but not in persons with Cushing syndrome or in some depressed persons. A stimulation test may assist in identifying adrenal insufficiency or conditions affecting the pituitary gland.

Cortisol:

• A.M.: 5–23 μg/dL or 138–635 nmol/L

• P.M.: 3–16 μg/dL or 83–441 nmol/L

• Midnight: <50% of a.m. level

• Newborns: 2–11 μg/dL or 55–304 nmol/L

• Maternal (at birth): 51.2–57.4 μg/dL or 1413–1584 nmol/L

• After the first week of life, cortisol levels attain adult values.

DST (low dose):

• 8:00 a.m. or 0800 hours following administration of dexamethasone: <5 μg/dL (a.m. value) or <138 nmol/L

Stimulation:

• Baseline: at least 5 μg/dL or 138 nmol/L

• After cosyntropin administration: rise of at least 10 μg/dL or 276 nmol/L

1. Obtain 5-mL venous blood samples at 8:00 a.m. (0800 hours) and at 4:00 p.m. (1600 hours). Serum is preferred. Heparin anticoagulant may be used. Label the specimen with the patient’s name, date and time of collection, and test(s) ordered. Place the specimen in a biohazard bag.

2. Observe standard precautions.

1. Decreased cortisol levels are found in the following conditions:

   1. Adrenal hyperplasia

   2. Addison disease (primary cortisol deficiency)

   3. Anterior pituitary hyposecretion (pituitary destruction)

   4. Hypothyroidism (hypopituitarism)

2. Increased cortisol levels are found in the following conditions:

   1. Hyperthyroidism

   2. Stress (trauma, surgery)

   3. Carcinoma (extreme elevation in the morning and no variation later in the day)

   4. Cushing syndrome (high on rising but no variation later in the day)

   5. Overproduction of ACTH due to tumors (oat cell cancers)

   6. Adrenal adenoma

   7. Obesity

Pretest Patient Care

1. Explain test purpose and blood-drawing procedure. Blood must be drawn at 8:00 a.m. (0800 hours) and 4:00 p.m. (1600 hours).

2. Encourage relaxation.

3. Ensure that no radioisotopes are administered within 1 day before the test.

4. Follow guidelines in Chapter 1 for safe, effective, informed pretest care.

1. Pregnancy will cause an increased value.

2. There is no normal diurnal variation in patients under stress.

3. Drugs such as spironolactone and oral contraceptives will give falsely elevated values (see Appendix E).

4. Decreased levels occur in persons taking dexamethasone, prednisone, or prednisolone (steroids) (see Appendix E).

5. Random cortisol tests are useless and provide no pertinent information.