Adrenocortical Hormone Tests Health Article

Definition

Adrenocortical hormone tests measure levels of aldosterone and cortisol (also known as hydrocortisone) in blood and urine. These hormones are synthesized from cholesterol by the action of several enzymes. The cells responsible are located in the outer part (cortex) of the adrenal glands, two small organs, one sitting just above each kidney. As steroid hormones, they are an important part of the body's endocrine system and help to regulate body functions. The adrenal cortex also produces many other steroid hormones including androgens, primarily dehydroepiandrosterone (DHEA) and androstenedione, that are converted to testosterone and dihydrotestosterone.

Aldosterone, a mineralcorticoid, helps regulate the amounts of sodium and potassium in the blood and, because fluid follows sodium, helps maintain fluid balance and blood volume, which, in turn, affect blood pressure.

Cortisol, a glucocorticoid, helps regulate the metabolism of proteins, fats, and carbohydrates, especially glucose (sugar). Specifically, cortisol helps convert amino acids (subunits of proteins) into glucose within the liver. It raises blood sugar levels by stimulating the release of glucose from cellular glucose stores and simultaneously acts to inhibit insulin, which moderates glucose transport into the cells. Cortisol also has a number of anti-inflammatory effects, including suppressing the immune system and reducing fever.

Purpose

Aldosterone measurement is used to detect aldosteronism (hyperaldosteronism), which is the excess secretion of the hormone by the adrenal glands. It is also used to detect those cases of hypoaldosteronism that occur in the absence of a low cortisol.

The cortisol test is performed on patients who are suspected to have malfunctioning adrenal glands. It is considered to be the best indicator of adrenal activity. Blood and urine cortisol measurements, together with the determination of ACTH levels, are the three most important tests in the investigation of Cushing's syndrome (overproduction of cortisol) and Addison's disease (underproduction of cortisol). Additional tests called simulation and suppression tests may be needed to detect disease in difficult cases, or to distinguish between the causes.

Precautions

Adrenocorticol function tests may be done on serum or urine. The nurse or phletotomist performing venipuncture should observe universal precautions for the prevention of transmission of bloodborne pathogens. Cortisol levels in blood are subject to diurnal variation. Test results must be evaluated with regard to the time of day the blood was collected. Physicians will determine if patients whose fluid balance may already be compromised by illness can undergo 24-hour urine tests. Physicians will also determine if patients can discontinue taking drugs that control sodium and potassium levels and fluid balance prior to testing. These tests are sometimes performed by a method called radioimmunoassay (RIA) that tags test reagents with radioactive iodide. RIA based tests may be contraindicated for patients who have had recent procedures using radiation or who have had radioactive drugs administered, because results may be altered and unreliable.

Aldosterone

Normal results for the aldosterone assay are laboratory-specific and vary according to test methodology used and the source of the specimen. Blood plasma levels, urine levels, and adrenal vein levels will be different. Results will also vary between patients depending upon average sodium intake, time of day, source of specimen, age, sex, and posture. Reference ranges are shown below for radioimmunoassay, the most common assay method for aldosterone.

Reference ranges for blood plasma levels:

• Supine (lying down): 3-10 ng/dL.
• Upright (sitting for at least two hours): Female: 5-30ng/dL; Male: 6-22 ng/dL.

Reference ranges for urine: 2-80 micrograms/24 hr.

Abnormal results. Increased levels of aldosterone are found in Conn's disease (aldosterone-producing adrenal tumor), and in Bartter's syndrome (overexcretion of potassium, sodium, and chloride by the kidneys resulting in low blood levels of potassium and high blood levels of aldosterone and renin). Elevated levels are also seen in secondary aldosteronism (in primary conditions such as congestive heart failure, cirrhosis of the liver, certain kidney diseases, hyperkalemia, a sodium-depleted diet, and toxemia of pregnancy), stress, and malignant hypertension.

Decreased levels of aldosterone are found in aldosterone deficiency, steroid therapy, high-sodium diets, certain antihypertensive therapies, and Addison's disease (an autoimmune disorder also involving abnormal cortisol and ACTH levels).