What Is an Ammonia Test?

Medically Reviewed by Kumar Shital, DO on September 12, 2023
3 min read

It’s a simple blood test that lets your doctor measure how much ammonia is in your blood. Bacteria in your gut and in your cells create ammonia when your body breaks down protein.

Ammonia is a waste product. Your liver turns ammonia into a chemical called urea. This chemical is water-soluble -- that means it dissolves in water. It leaves your body in your urine. But if you have certain health conditions, like kidney or liver failure, your body can’t make or get rid of urea. In either case, ammonia builds up. This can cause a number of problems, like confusion, extreme tiredness, and in some cases, coma or even death.

Your doctor will probably order an ammonia test if you have neurological changes, like sudden confusion or you fall into a coma for no reason.

For a newborn, your doctor might order an ammonia test if they have the following symptoms within the first few days after birth:

Your doctor might order this test for your infant or young child if they suspect your child has any of the following:

  • Reye’s syndrome, a rare but serious illness that can affect the liver and brain. It’s linked to aspirin use in kids, which has declined since the 1980s.
  • Urea cycle disorder. This affects how your body gets rid of waste made from breaking down protein. In newborns, it presents as vomiting, lack of energy, irritability, or seizures.

Other reasons your doctor might order this test include:

  • You have liver disease or your blood work suggests you do, and your health takes a turn for the worse (especially if you have altered brain function or a neurologic problem).
  • They want to find out if treatment is working for a condition called hepatic encephalopathy. That’s when people who have liver disease have extreme confusion and other mental changes.

A lab tech will take a blood sample from a vein in your arm. They might also take blood from an artery, rather than a vein. But that’s not done as often.

You shouldn’t exercise or smoke cigarettes before the test. Tell your doctor about all medicines, herbs, vitamins, and supplements you take -- even aspirin and over-the-counter medicines.

High ammonia levels sometimes point to either liver or kidney disease. But several other things can cause higher ammonia levels, like:

  • Bleeding in your stomach, intestines, esophagus, or other parts of your body
  • Alcohol and drug use, including narcotics and medicines that take extra fluid out of your body (diuretics)
  • Smoking
  • Recent exercise -- muscles make ammonia when they are active
  • Tourniquet use -- increases the level of blood ammonia

A low level of ammonia could be caused by very high blood pressure that comes on quickly and suddenly.

Your test may come back too high or too low but that may not mean there is anything wrong. That’s because sometimes, the way the lab does the test affects the result. It’s best to talk to your doctor about what your results mean.