How Performed: Adult or child:
Blood is drawn from a vein (venipuncture), usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and a tourniquet (an elastic band) or blood pressure cuff is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the tourniquet to distend (fill with blood). A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. During the procedure, the tourniquet is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.

Infant or young child:
The area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. Cotton or a bandage may be applied to the puncture site if there is any continued bleeding.

Sometimes normal saline is ingested (or given through an IV) for 2 to 4 hours before blood is drawn; or a diuretic may be given and upright posture maintained for 4 hours before the test.

How To Prepare: Instructions may include eating a normal-sodium diet for at least 2 weeks before the test.

Women may need to specify the phase of their menstrual cycle because it affects the test results.

You should avoid, if possible, potentially-interfering drugs or factors (See special considerations).

Infants and children:
The physical and psychological preparation you can provide for this or any test or procedure depends on your child’s age, interests, previous experience, and level of trust. For specific information regarding how you can prepare your child, see the following topics as they correspond to your child’s age:

• infant test or procedure preparation (birth to 1 year)
• toddler test or procedure preparation (1 to 3 years)
• preschooler test or procedure preparation (3 to 6 years)
• schoolage test or procedure preparation (6 to 12 years)
• adolescent test or procedure preparation (12 to 18 years)

How It Feels: When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.

Risks:

• excessive bleeding
• fainting or feeling lightheaded
• hematoma (blood accumulating under the skin)
• infection (a slight risk any time the skin is broken)
• multiple punctures to locate veins

Why Performed: This test is performed when an abnormality of aldosterone levels is suspected.

Aldosterone is a hormone released by the adrenal glands. It is part of the complex mechanism used by the body to regulate blood pressure. Aldosterone increases the reabsorption of sodium and the excretion of potassium in the distal tubules of the kidneys. The reabsorption of sodium is accompanied by the reabsorption of water, which raises blood pressure.

Normal Values: supine: 2 to 16 ng/dl
upright: 5 to 41 ng/dl

Note: ng/dl = nanograms per deciliter

Abnormal Results: Greater-than-normal levels of aldosterone may indicate:

• primary hyperaldosteronism (rare)
• Bartter’s syndrome (extremely rare)
• Cushing’s syndrome (rare)
• edema related to congestive heart failure
• malignant hypertension
• nephrotic syndrome
• renal ischemia (reduced blood flow to the kidneys)

• Addison’s disease (rare)
• toxemia of pregnancy

Cost:

Special Considerations: Factors that can affect aldosterone measurements include strenuous exercise, acute stress, a high- or low-sodium diet, and pregnancy.

Drugs that can increase aldosterone measurements include diazoxide, hydralazine, and nitroprusside.

Drugs that can decrease aldosterone measurements include fludrocortisone and propranolol.

Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.