At a glance
Also known as
Why get tested?
To detect an elevated level of ammonia in the blood that may be caused by severe liver disease or genetic disorders affecting the formation of urea; to investigate changes in consciousness; to help diagnose hepatic (liver) encephalopathy (altered consciousness due to liver failure) or Reye’s syndrome (a serious condition that causes swelling in the liver and brain).
When to get tested?
When a person with liver disease has mental changes or goes into a coma; when an infant has frequent vomiting and increased lethargy or when a child has persistent vomiting and unusual sleepiness about a week after a viral illness
A blood sample drawn from a vein or artery in your arm
Test preparation needed?
What is being tested?
Ammonia is a waste product produced primarily by gut bacteria during protein digestion. A waste product, ammonia is normally transported to the liver, where it is converted into urea. The urea is then carried by the blood to the kidneys, where it is excreted in the urine. If ammonia is not efficiently converted to urea (‘urea cycle’) by the liver it builds up in the blood and passes into the brain.
In the brain, ammonia and other compounds normally processed by the liver can cause hepatic (liver) encephalopathy – 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. If left untreated, they may experience seizures, have difficulty breathing, and may fall into a coma.
Problems with ammonia processing can arise from several sources, including:
- Rare inherited defects in the urea cycle – a deficiency or defect in one or more of the necessary to complete the conversion of ammonia to urea
- Severe liver disease – damage limits the ability of the liver to metabolise ammonia. Sudden increases in ammonia may be seen in patients with stable liver disease, especially following a triggering event such as a bleed in the stomach.
- Decreased blood flow to the liver – ammonia is less able to be processed by the liver Drugs – some drugs e.g. the antiepileptic valproate may sometimes lead to increased ammonia. Aspirin is thought to be involved in Reye’s syndrome, a cause of increased ammonia in children.
How is the sample collected for testing?
A blood sample is obtained by inserting a needle into a vein or artery in the arm. The sample should be sent to the laboratory promptly for processing and analysis.
Is any test preparation needed to ensure the quality of the sample?
Avoid smoking cigarettes prior to blood collection.
Is ammonia testing used to detect or monitor ammonia poisoning?
No, it is not considered clinically useful. In most cases, ammonia acts locally, burning or irritating whatever it comes in contact with but, according to the Agency for Toxic Substances and Disease Registry (ATSDR), it does not usually act as a systemic poison. Concentrated commercial ammonia, in a liquid or vapour form, causes more severe burns than the more dilute liquid household ammonia, but both can cause damage to the eyes, skin, respiratory tract, and to the mouth, throat and stomach if swallowed.