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Also known as: NH3
Formal name: Ammonia, plasma

Board approvedAll content on Lab Tests Online has been reviewed and approved by our Editorial Review Board.

The Test Sample

What is being tested?

Ammonia is a waste product formed primarily by bacteria in the intestines during the digestion of protein. If not processed and cleared from the body appropriately, excess ammonia can accumulate in the blood. This test measures the amount of ammonia in the blood.

Ammonia is normally transported in the blood to the liver, where it is converted into two substances called urea and glutamine. The urea is then carried to the kidneys, where it is eliminated in the urine. If this "urea cycle" does not complete the breakdown of ammonia, ammonia builds up in the blood and can pass from the blood into the brain.

Ammonia is toxic to the brain. For example, when liver function is significantly reduced due to disorders such as cirrhosis or hepatitis, ammonia and other compounds processed by the liver can accumulate in the brain and cause a condition called hepatic encephalopathy.

Hepatic encephalopathy causes mental and neurological changes that can lead to confusion, disorientation, sleepiness, and eventually to coma and even death.

Infants and children with increased ammonia levels may vomit frequently, be irritable, and be increasingly lethargic. Left untreated, they may experience seizures, have difficulty breathing, and may lapse into a coma.

Problems with ammonia processing can arise from conditions such as:

  • Severe liver disease – damage limits the ability of the liver to process ammonia; spikes in ammonia blood levels may be seen in people with stable liver disease, especially following a triggering event such as gastrointestinal bleeding or an electrolyte imbalance.
  • Decreased blood flow to the liver – ammonia is less able to get to the liver to be processed.
  • Reye syndrome – a rare condition that affects the blood, brain, and liver; it is characterized by a rise in ammonia levels and a fall in glucose. It affects primarily children and young adults. In most cases, it follows and appears to be triggered by a viral infection, such as the flu or chickenpox. Children who are given aspirin are at an increased risk.
  • Renal failure – the kidneys are unable to effectively rid the body of urea, leading to a build-up of ammonia in the blood.
  • Rare inherited defects in the urea cycle – a deficiency or defect in one or more of the enzymes necessary to complete the conversion of ammonia to urea.

How is the sample collected for testing?

A blood sample is obtained by inserting a needle into a vein 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 you are given.