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, sleepiness, and eventually coma and even death. Infants and children with increased ammonia levels 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 levels may be seen in patients with stable liver disease, especially following a event such as a bleed in 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 levels 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, 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.