Test Overview

An aldosterone test measures the level of aldosterone (a hormone made by the adrenal glands), in the blood. Aldosterone helps regulate sodium and potassium levels in the body. This helps control blood pressure and the balance of fluids and electrolytes in the blood.

The kidney hormone renin normally stimulates the adrenal glands to release aldosterone. High levels of both renin and aldosterone are normally present when the body is trying to conserve fluid and salt (sodium). When a tumour that makes aldosterone is present, your aldosterone level will be high while a renin level will be low. Usually a renin activity test is done when the aldosterone level is measured.

Why It Is Done

An aldosterone test is done to:

• Measure the amount of aldosterone released into the body by the adrenal glands.
• Check for a tumour in the adrenal glands.
• Find the cause of high blood pressure or low blood potassium levels. This is done when overactive adrenal glands or an abnormal adrenal growth are suspected.

How To Prepare

An aldosterone test is often done at the time of a routine blood test. You don't need to do anything before having routine blood tests.

If you are having follow-up aldosterone blood tests, your doctor may give you the following instructions:

• Eat foods with a normal amount of sodium (2,300 mg per day) for 2 weeks before the test. Do not eat foods that are very salty, such as bacon, canned soups and vegetables, olives, bouillon, soy sauce, and salty snacks like potato chips or pretzels. A low-salt diet can also increase aldosterone levels. Tell your doctor if you are on a low-salt food plan.
• Do not eat natural black licorice for 2 weeks before this test.

Many medicines may change the results of this test. Be sure to tell your doctor about all the non-prescription and prescription medicines you take. You may be asked to stop taking some medicines for 2 weeks before the test. These include hormones (such as progesterone and estrogens), corticosteroids, diuretics, and many medicines used to treat high blood pressure, especially spironolactone (Aldactone), eplerenone (Inspra), and beta-blockers.

The amount of aldosterone in blood changes depending on whether you are standing up or lying down. If your results show a problem, repeat tests may be done in different positions and under different conditions, such as not eating before the test or eating foods that contain a specific amount of salt. Your doctor may ask you to have your blood drawn at a certain time. That's because aldosterone levels are highest in the early morning.

How It Is Done

A health professional uses a needle to take a blood sample, usually from the arm.

How It Feels

When a blood sample is taken, you may feel nothing at all from the needle. Or you might feel a quick sting or pinch.

Risks

There is very little chance of having a problem from this test. When a blood sample is taken, a small bruise may form at the site.

Results

Results are usually available in 2 to 5 days.

Normal

Each lab has a different range for what's normal. Your lab report should show the range that your lab uses for each test. The normal range is just a guide. Your doctor will also look at your results based on your age, health, and other factors. A value that isn't in the normal range may still be normal for you.

High values

High aldosterone levels can be caused by:

• A tumour in the adrenal glands (Conn's syndrome).
• Kidney disease.
• Liver disease.
• Heart failure.
• Dehydration.
• A condition during pregnancy that causes high blood pressure (pre-eclampsia).

An overgrowth of normal cells in the adrenal glands (called adrenal hyperplasia) or a tumour of the adrenal glands affects the adrenal glands directly and causes a condition called primary aldosteronism. Certain diseases, such as heart failure, cirrhosis, and kidney disease, can also cause high aldosterone levels, but this is a normal response by the adrenal glands. These diseases cause secondary aldosteronism.

Low values

Addison's disease and some types of kidney disease may cause low aldosterone levels.