Test Overview

An ammonia test measures the amount of ammonia in the blood. Most ammonia in the body forms when protein is broken down by bacteria in the intestines. The liver normally converts ammonia into urea, which is then eliminated in urine.

Ammonia levels in the blood rise when the liver is not able to convert ammonia to urea. This may be caused by cirrhosis or severe hepatitis.

For this test, a blood sample may be taken from either a vein or an artery.

Why It Is Done

An ammonia test is done to:

• Check how well the liver is working, especially when symptoms of confusion, excessive sleepiness, coma, or hand tremor are present.
• Check the success of treatment for severe liver disease, such as cirrhosis.
• Help identify a childhood disorder called Reye syndrome that can damage the liver and the brain. Ammonia testing can also help predict the outcome (prognosis) of a diagnosed case of Reye syndrome.
• Help predict the outcome (prognosis) of a diagnosed case of acute liver failure.
• Check the level of ammonia in a person receiving high-calorie intravenous (IV) nutrition (hyperalimentation).

How To Prepare

Do not eat, drink anything other than water, or smoke for 8 hours before having an ammonia blood test. And avoid strenuous exercise just prior to having this test.

How It Is Done

If the sample is taken from a vein

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

If the sample is taken from an artery

A sample of blood from an artery is usually taken from the inside of the wrist (radial artery). But it can also be taken from an artery in the groin (femoral artery) or on the inside of the arm above the elbow crease (brachial artery). You will be seated with your arm extended and your wrist resting on a small pillow. The health professional drawing the blood may rotate your hand back and forth and feel for a pulse in your wrist.

To prevent the chance of damaging the artery of the wrist when the blood sample is taken, a procedure called the Allen test may be done to make sure that blood flow to your hand is normal. An ammonia test will not be done on an arm used for dialysis or if there is an infection or inflammation in the area of the puncture site.

The health professional taking a sample of your blood will:

• Clean the needle site with alcohol. You may be given an injection of local anesthetic to numb that area.
• Put the needle into the artery. More than one needle poke may be needed.
• Allow the blood to fill the syringe. Be sure to breathe normally while your blood is being collected.
• Put a gauze pad or cotton ball over the needle site as the needle is removed.
• Put a bandage over the puncture site and apply firm pressure for 5 to 10 minutes (or maybe longer if you take blood-thinning medicine or have bleeding problems).

Watch

How It Feels

If the sample is taken from a vein

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

If the sample is taken from an artery

Collecting blood from an artery is more painful than collecting it from a vein. That's because the arteries are deeper and are protected by nerves.

• Most people feel a brief, sharp pain as the needle to collect the blood sample enters the artery. If you are given a local anesthetic, you may feel nothing at all from the needle puncture, or you may feel a brief sting or pinch as the needle goes through the skin.
• You may feel more pain if the person drawing your blood has a hard time finding your artery, your artery is narrowed, or you are very sensitive to pain.

Risks

If the sample is taken from a vein

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.

If the sample is taken from an artery

There is little chance of a problem from having a blood sample taken from an artery.

• You may get a small bruise at the site. You can lower the chance of bruising by keeping pressure on the site for at least 10 minutes after the needle is removed (longer if you have bleeding problems or take blood thinners).
• You may feel light-headed, faint, dizzy, or nauseated while the blood is being drawn from your artery.
• In rare cases, the needle may damage a nerve or the artery, causing the artery to become blocked.

Though problems are rare, be careful with the arm or leg that had the blood taken. Do not lift or carry objects for about 24 hours after you have had blood taken from an artery.

Results

Results are usually available within 12 hours.

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 levels of ammonia in the blood may be caused by:

• Liver disease, such as cirrhosis or hepatitis.
• Reye syndrome.
• Heart failure.
• Kidney failure.
• Severe bleeding from the stomach or intestines.

High ammonia values in a baby may be present when the blood types of a mother and her baby do not match (hemolytic disease of the newborn).