At a Glance
Why Get Tested?
To detect elevated concentrations of ammonia in the blood, to help diagnose severe liver disease and certain genetic urea cycle disorders, to investigate changes in consciousness, or to help diagnose hepatic encephalopathy and Reye’s syndrome
When to Get Tested?
If a patient experiences mental changes or lapses into a coma of unknown origin; if an infant or child experiences frequent vomiting and increased lethargy as a newborn or about a week after a viral illness
A blood sample taken from a vein or artery in your arm
Test Preparation Needed?
Avoid smoking cigarettes prior to collection of the specimen and follow any other instructions that you are given
The Test Sample
What is being tested?
This test measures the concentration of ammonia in the blood. Ammonia is a chemical produced by bacteria in the intestine and by cells in the body during the processing of proteins. Ammonia is a poisonous waste product which is normally transported to the liver, and then converted into two chemicals called urea and glutamine. The urea is then carried by the blood to the kidneys, where it is excreted in the urine. If this does not work correctly, ammonia can build up in the blood and pass into the brain.
Accumulation of ammonia and other compounds normally broken down by the liver can cause a condition affecting the brain called hepatic encephalopathy. This causes symptoms such as confusion, disorientation, drowsiness, and eventually coma and even death. Infants and children with increased blood ammonia concentrations may vomit frequently, be irritable, and be increasingly tired. If left untreated, they may develop seizures, breathing difficulty, and fall into a coma.
Problems with ammonia processing can arise for several reasons, including:
- Rare inherited defects in the urea cycle - a deficiency or inborn genetic defect affecting one or more of the enzymes necessary to complete the conversion of ammonia to urea.
- Severe liver disease - damage which reduces the ability of the liver to breakdown and remove ammonia. Sudden increases in blood ammonia concentration may be seen in patients with stable liver disease, especially following an event such as a bleed into the stomach or elsewhere in the intestine or an imbalance in sodium or other electrolytes.
- Decreased blood flow to the liver such that ammonia is less able to be removed.
- Reye’s syndrome - a rapidly developing condition that affects the blood, brain, and liver. It typically produces a rise in ammonia and a fall in glucose and affects children and young adults. In most cases, it follows and appears to be triggered by a viral infection. Children who use aspirin are at an increased risk.
- Kidney failure - the kidneys are unable to effectively remove the body’s urea, leading to a build-up of ammonia in the blood.
How is the sample collected for testing?
A blood sample is obtained by inserting a needle into a vein or artery in the arm.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
Is any test preparation needed to ensure the quality of the sample?
Avoid smoking cigarettes prior to collection of the specimen and follow any other instructions that you are given.
Ask a Laboratory Scientist
NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.