Ammonia blood test
Quick answer: An ammonia test measures ammonia, a waste product normally cleared by the liver, in your blood. Doctors order it when someone with liver disease becomes confused or drowsy, or in babies with suspected metabolic problems.
- SampleBlood
- TakesAbout 5 minutes
- Before the testAvoid smoking and heavy exercise before the test; the sample must reach the lab quickly on ice.
How the test is done
- 1You avoid smoking and heavy exercise before the test
- 2A tourniquet is used for as short a time as possible
- 3Blood is drawn into a tube that is placed on ice
- 4The sample is sent to the lab right away
What your results can mean
Reading your report
Normal ranges differ between labs and by age and sex, so discuss your result with your doctor.
If the result is outside the usual range
A high level can be seen with serious liver disease, some inherited metabolic disorders in babies, and with certain medicines. Delays in handling the sample can also falsely raise it.
Who usually has this test
People with liver disease who become confused or drowsy, and babies or children with unexplained vomiting, sleepiness or seizures.
Risks and aftercare
There may be slight bruising at the needle site.
Names and options
Also called: blood ammonia, plasma ammonia
Listed by the hospital as
- AMMONIA, EDTA PLASMA
Questions about this test
Why is the ammonia sample put on ice?
Ammonia keeps forming in a blood sample left at room temperature, which can give a falsely high result. Ice and quick testing help prevent this.
How is high ammonia linked to confusion?
When the liver cannot clear ammonia, it builds up and affects the brain. This can cause confusion, drowsiness or changes in behaviour, called hepatic encephalopathy.
Can smoking affect the ammonia test?
Yes, smoking just before the test can raise the level. Avoid smoking for several hours beforehand if you can.
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This page explains each test in general terms so you know what to expect. It is not medical advice: your doctor decides which tests you need and what your results mean. Reference ranges differ between laboratories. Updated 4 November 2026.