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Ammonia Test

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).

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.


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.

Don't lift or carry objects for about 24 hours after you have had blood taken from an artery.


Results are usually available within 12 hours.


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:

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).


Current as of: September 8, 2022

Author: Healthwise Staff
Medical Review:
E. Gregory Thompson MD - Internal Medicine
Adam Husney MD - Family Medicine
Martin J. Gabica MD - Family Medicine
Jerome B. Simon MD, FRCPC, FACP - Gastroenterology