Blood test
Ammonia Blood Test
An ammonia blood test measures ammonia, a waste product that can build up when the liver is not working properly or in certain metabolic disorders.
Quick answer
Ammonia Blood Test: what it is and what the results mean
Ammonia is a waste product made when the body breaks down protein. The liver normally converts it to urea for removal.
- Why it is done: It is used to investigate confusion or altered consciousness in people with liver disease (hepatic encephalopathy), and to help diagnose certain inherited metabolic disorders, especially in children.
- Understanding results: A raised ammonia can support a diagnosis of hepatic encephalopathy or a metabolic disorder, but levels do not always match how unwell someone is.
What it is
Ammonia is a waste product made when the body breaks down protein. The liver normally converts it to urea for removal. A blood test measures ammonia, which can build up if the liver fails or in some inherited metabolic conditions.
Why it is done
It is used to investigate confusion or altered consciousness in people with liver disease (hepatic encephalopathy), and to help diagnose certain inherited metabolic disorders, especially in children.
What to expect
It is a blood test from a vein in the arm, but the sample must be handled carefully and quickly (often kept cold and processed promptly) because ammonia levels can change if the sample is delayed.
Understanding the results
A raised ammonia can support a diagnosis of hepatic encephalopathy or a metabolic disorder, but levels do not always match how unwell someone is. Results are interpreted alongside symptoms and other liver and metabolic tests.
Good to know
Risks and limitations
The blood test is safe, but results can be falsely raised by sample handling problems, so careful collection is important. Ammonia levels do not perfectly reflect brain effects, so they are one part of the assessment.
Education and reference only. This explains the test in general terms and is not medical advice. Always follow the specific instructions from the team arranging your test, and discuss your results with your clinician.
Answers
Ammonia Blood Test: frequently asked questions
Why does ammonia need to be handled carefully in the lab?
Ammonia levels can rise in a sample if it is not kept cold and processed quickly, which could give a falsely high result. Careful, prompt handling ensures an accurate measurement.
Does a high ammonia always cause confusion?
Not exactly. Although raised ammonia is linked to confusion in liver disease, the level does not always match how unwell a person is, so it is interpreted alongside symptoms.
Related tests
Other blood test investigations
Sources
Where this is drawn from
- NHS — Tests and treatments
- NICE — diagnostic guidance
- Association for Laboratory Medicine / relevant professional body
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