Aldosteron

Test Description

Aldosterone is a mineralocorticoid secreted by the adrenal cortex. The release of

aldosterone is controlled primarily by the renin-angiotensin-aldosterone system. A

decrease in extracellular fluid results in decreased blood flow through the kidneys,

which in turn stimulates production and secretion of renin by the kidneys. Renin acts

on angiotensinogen to form Angiotensin I which, in the presence of angiotensinconverting

enzyme (ACE), is converted to Angiotensin II. Angiotensin II stimulates the

adrenal cortex to increase aldosterone production. The effects of aldosterone occur in

the renal distal tubule, where it causes increased reabsorption of sodium and chloride

and increased excretion of potassium and hydrogen ions. The result of these actions

is retention of increased water and an increase in extracellular fluid. The ultimate

effect of changes in aldosterone level is regulation of blood pressure.

Measurement of aldosterone level is performed on both the plasma and the

urine. This information assists in the diagnosis of primary aldosteronism, caused by

an abnormality of the adrenal cortex, and of secondary aldosteronism, which may

result from overstimulation of the adrenal cortex by a substance such as angiotensin

or ACTH.

THE EVIDENCE FOR PRACTICE

Primary hyperaldosteronism may account for up to 15% of patients with hypertension, particularly

in middle age. The use of the random serum aldosterone/plasma renin activity ratio

(ARR) with a sufficiently high cutoff value has facilitated diagnosis at an acceptable cost

and low risk.

Normal Values

Plasma, standing:                        4–31 ng/dL    (111–860 pmol/L SI units)

Plasma, recumbent:                    <16 ng/dL       (<444 pmol/L SI units)

Urinary excretion:                      6–25 mcg/day (17–69 nmol/day SI units)

Possible Meanings of Abnormal Values

Increased                                                             Decreased

Adrenal cortical hyperplasia                                 Addison’s disease

Aldosterone-producing adenoma                         High-sodium diet

Cirrhosis of liver with ascites                              Hypernatremia

Congestive heart failure                                       Hypokalemia

Hemorrhage                                                         Salt-losing syndrome

Hyperkalemia                                                      Septicemia

Hyponatremia                                                      Toxemia of pregnancy

Hypovolemia

Low-sodium diet

Malignant hypertension

Nephrosis

Nephrotic syndrome

Potassium loading

Pregnancy

Primary hyperaldosteronism (Conn’s syndrome)

Stress

Contributing Factors to Abnormal Values

• Test results may be altered by diet, exercise, licorice ingestion, and posture.

• Drugs that may increase aldosterone levels: corticotropin, diazoxide, diuretics,

   hydralazine hydrochloride, nitroprusside sodium, oral contraceptives, potassium.

• Drugs that may decrease aldosterone levels: fludrocortisone acetate, methyldopa,

nonsteroidal anti-inflammatory drugs, propranolol, steroids.

Interventions/Implications

Pretest

• Explain to the patient the purpose of the test and the need for a blood sample to be drawn.

   Explain the effect of the upright position on the test results.

• No fasting is required before the test.

• Unless otherwise ordered, instruct the patient to follow a 3-g sodium diet for at least 2 weeks

   before the test. Explain to the patient that this is considered “normal” sodium intake.

• Explain 24-hour urine collection procedure to the patient.

• Stress the importance of saving all urine in the 24-hour period. Instruct the patient to

   avoid contaminating the urine with toilet paper or feces.

• Inform the patient of the presence of a preservative in the collection bottle.

• If possible, drugs that may affect test results should be withheld for at least 2 weeks

before the test.

Procedure

Blood sampling

• A 7-mL blood sample is drawn in a plain red-top collection tube containing no gel. In

hospitalized patients, one blood sample is drawn while the patient is supine and another

is drawn 4 hours later after the patient has been upright and ambulating. For outpatients,

the blood sample is drawn after the patient has been upright for 2 hours.

• Gloves are worn throughout the procedure.

Urine collection

• Obtain the proper container containing 1 g of boric acid as preservative from the

  laboratory.

• Begin the testing period in the morning after the patient’s first voiding, which is

  discarded.

• Timing of the 24-hour period begins at the time the first voiding is discarded.

• All urine for the next 24 hours is collected in the container, which is to be kept refrigerated

   or on ice.

• If any urine is accidentally discarded during the 24-hour period, the test must be discontinued

   and a new test begun.

• The ending time of the 24-hour collection period should be posted in the patient’s room.

• Gloves are worn whenever dealing with the specimen collection.

Post test

• Apply pressure at venipuncture site. Apply dressing, periodically assessing for continued

   bleeding.

• Label the specimen and transport it to the laboratory.

• At the end of the 24-hour collection period, label and send the urine container on ice to

  the laboratory as soon as possible.

• Resume medications as taken before the testing period.

• Report abnormal findings to the primary care provider.