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Ammonia

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.

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?).

How It Is Done

If the sample is taken from a vein

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.

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 stick 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 (possibly longer if you take blood-thinning medicine or have bleeding problems).

How It Feels

If the sample is taken from a vein

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.

If the sample is taken from an artery

Collecting blood from an artery is more painful than collecting it from a vein 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 if you are very sensitive to pain.

Risks

If the sample is taken from a vein

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.

If the sample is taken from an artery

There is little chance of a problem from having 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 lightheaded, faint, dizzy, or nauseated while the blood is being drawn from your artery.
  • 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.
  • On rare occasions, 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 draw. Do not lift or carry objects for about 24 hours after you have had blood drawn from an artery.

Results

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

Normal

The normal values listed here—called a reference range—are just a guide. These ranges vary from lab to lab, and your lab may have a different range for what’s normal. Your lab report should contain the range your lab uses. Also, your doctor will evaluate your results based on your health and other factors. This means that a value that falls outside the normal values listed here may still be normal for you or your lab.

Ammonia1

Adults:

15–60 micrograms per deciliter (mcg/dL)

21–50 micromoles per liter (mcmol/L)

Children:

70–135 mcg/dL

41–80 mcmol/L

Newborns:

170–340 mcg/dL

100–200 mcmol/L

High values

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

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).

What Affects the Test

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 some diuretics (such as furosemide), acetazolamide, and valproate.
  • Using medicines that decrease ammonia levels, such as neomycin, tetracycline, diphenhydramine, isocarboxazid, phenelzine, and tranylcypromine, and lactulose.
  • Strenuous exercise just before the test.

What To Think About

  • 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.

References

Citations

  1. Fischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.

Other Works Consulted

  • Chernecky CC, Berger BJ (2008). Laboratory Tests and Diagnostic Procedures, 5th ed. St. Louis: Saunders.
  • Fischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.
  • Pagana KD, Pagana TJ (2010). Mosby’s Manual of Diagnostic and Laboratory Tests, 4th ed. St. Louis: Mosby.

Credits

By Healthwise Staff
Primary Medical Reviewer E. Gregory Thompson, MD - Internal Medicine
Specialist Medical Reviewer Jerome B. Simon, MD, FRCPC, FACP - Gastroenterology
Last Revised November 4, 2011

Last Revised: November 4, 2011

Author: Healthwise Staff

Medical Review: E. Gregory Thompson, MD - Internal Medicine & Jerome B. Simon, MD, FRCPC, FACP - Gastroenterology

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