Ammonia

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.

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's syndrome that can damage the liver and the brain. Ammonia testing can also help predict the outcome (prognosis) of a diagnosed case of Reye's 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).

Do not eat, drink anything other than water, or smoke for 8 hours before having an ammonia blood test.

Avoid strenuous exercise just prior to having this test.

Tell your doctor if you:

• Are taking any medicines. Many medicines can interfere with test results. Your doctor may instruct you to stop taking certain medicines for several days before having an ammonia test.
• Smoke or drink alcohol.

Talk to your doctor about any concerns you have regarding the need for the test, its risks, how it will be done, or what the results may mean. To help you understand the importance of this test, fill out the medical test information form(What is a PDF document?).

The health professional taking a sample of your blood will:

• Wrap an elastic band around your upper arm to stop the flow of blood. This makes the veins below the band larger so it is easier to put a needle into the vein.
• Clean the needle site with alcohol.
• Put the needle into the vein. More than one needle stick may be needed.
• Attach a tube to the needle to fill it with blood.
• Remove the band from your arm when enough blood is collected.
• Put a gauze pad or cotton ball over the needle site as the needle is removed.
• Put pressure on the site and then put on a bandage.

The blood sample is taken from a vein in your arm. An elastic band is wrapped around your upper arm. It may feel tight. You may feel nothing at all from the needle, or you may feel a quick sting or pinch.

There is very little chance of a problem from having blood sample taken from a vein.

• You may get a small bruise at the site. You can lower the chance of bruising by keeping pressure on the site for several minutes.
• In rare cases, the vein may become swollen after the blood sample is taken. This problem is called phlebitis. A warm compress can be used several times a day to treat this.
• Ongoing bleeding can be a problem for people with bleeding disorders. Aspirin, warfarin (Coumadin), and other blood-thinning medicines can make bleeding more likely. If you have bleeding or clotting problems, or if you take blood-thinning medicine, tell your doctor before your blood sample is taken.

An ammonia test measures the amount of ammonia in the blood. Results are usually available within 12 hours.

Normal

Normal values may vary from lab to lab.

High values

High levels of ammonia in the blood may be caused by:

• Liver disease, such as cirrhosis or hepatitis.
• Reye's 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).

Reasons you may not be able to have the test or why the results may not be helpful include:

• Smoking.
• Severe constipation.
• Eating a high-protein or a low-protein diet.
• Using medicines that increase blood ammonia levels, such as heparin, some diuretics (such as furosemide), acetazolamide, and valproic acid.
• Using medicines that decrease ammonia levels, such as neomycin, tetracycline, diphenhydramine, isocarboxazid (Marplan), phenelzine (Nardil), and tranylcypromine (Parnate), heparin, and lactulose.
• Strenuous exercise just before the test.

• Ammonia levels do not always reflect the severity of a person's symptoms. For example, a person with severe cirrhosis may have only slightly elevated blood ammonia levels and yet may not be thinking clearly or may be sleepy or in a coma. Other people with very high ammonia levels may think and act normally.
• Symptoms of a high ammonia level, such as confusion or extreme sleepiness, may be treated with a medicine called lactulose, a laxative that works by reducing ammonia production in the intestines.
• It is common for newborns to have slightly high levels of ammonia in their blood. But the levels are temporary and usually do not cause symptoms.

Other Works Consulted

• Chernecky CC, Berger BJ, eds. (2004). Laboratory Tests and Diagnostic Procedures, 4th ed. Philadelphia: Saunders.

• Fischbach FT, Dunning MB III, eds. (2004). Manual of Laboratory and Diagnostic Tests, 7th ed. Philadelphia: Lippincott Williams and Wilkins.

• Pagana KD, Pagana TJ (2002). Mosby’s Manual of Diagnostic and Laboratory Tests, 2nd ed. St. Louis: Mosby.