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Ammonia Levels

What is an ammonia levels test?

An ammonia levels test measures the amount of ammonia in a sample of your blood. Ammonia is also called NH3. It is a normal waste product in your body. Healthy bacteria in your intestines make ammonia when you digest protein in the foods you eat.

Normally, your liver changes ammonia into another waste product called urea. Your kidneys get rid of urea in urine (pee). This process is called the urea cycle.

When you're healthy, the urea cycle prevents ammonia from building up in your blood. This is very important because ammonia is toxic (poisonous) to your brain. Even small increases in the level of ammonia in your blood can cause permanent brain damage, coma, and even death.

Liver disease is the most common cause of high ammonia levels. Other causes include kidney failure and genetic disorders called urea cycle disorders.

The medical term for high ammonia levels is hyperammonemia.

Other names: NH3 test, blood ammonia test, serum ammonia, ammonia; plasma

What is it used for?

An ammonia levels test may be used to help diagnose high ammonia levels in people who have symptoms. The test alone can't diagnose conditions that increase the amount of ammonia in your blood. But it may be used with other tests to help find the cause.

Ammonia levels testing can help diagnose conditions such as:

  • Hepatic encephalopathy. This condition happens when toxins (poisons), including ammonia, build up in your brain because your liver is unable to break them down. It can cause memory loss, confusion, loss of consciousness, and coma.
  • Reye syndrome. This rare disease damages the brain and liver. Without treatment, it causes death. It mostly happens in children younger than 15 who have had a viral infection that causes a fever, such as chickenpox or the flu. Taking aspirin during a viral illness may increase the risk of Reye syndrome.
  • Urea cycle disorders (UCDs). This is a group of rare genetic conditions that you inherit from your parents. If you have a UCD, you lack enzymes that help change ammonia into urea. An enzyme is a protein that speeds up certain chemical reactions in your body. Symptoms may show up shortly after birth or later in life. Newborns are tested for certain UCDs as part of routine newborn screening. Your child's health care provider can explain more about which UCD screening tests are used in your state.

Ammonia levels testing is also used to monitor conditions that cause high ammonia levels and to check if treatment is working.

Why do I need an ammonia levels test?

You may need this test if you have symptoms that could be from too much ammonia in your blood. The symptoms depend on how high your ammonia levels are and your age. Symptoms in children and adults may include:

  • Feeling irritable
  • Lack of energy and mental alertness or being very sleepy
  • Vomiting
  • Headache
  • Loss of muscle coordination that may cause difficulties with walking or speech
  • Changes in behavior
  • Confusion, including not being sure about the time and/or where or who you are
  • Mood swings
  • Seizures

Other symptoms in children may include:

  • Not growing taller or gaining weight as expected
  • Lack of muscle tone (limp muscles)
  • Developmental delays in children or infants

Newborn babies may develop symptoms of high ammonia levels within three days after birth. Symptoms in newborns include the above symptoms and may also include fast breathing and/or making grunting sounds when breathing. If your baby or child has any symptoms of high ammonia levels, contact their provider right away.

If you have a family history of genetic urea cycle disorders, you or your child may need this test even if you don't have symptoms.

If you've been diagnosed with high ammonia levels, you may need this test to see how well your treatment is working.

What happens during an ammonia levels test?

In most cases, a health care professional will take a blood sample from a vein in your arm, using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out. This usually takes less than five minutes.

In certain cases, the blood sample may be taken from an artery, which is a blood vessel that carries blood from your heart to the rest of your body. Some providers think blood from an artery may provide more accurate results. The blood is taken from an artery in your wrist, arm, or groin using a needle attached to a syringe.

Taking blood from an artery tends to be more uncomfortable than blood tests that use a vein. So, numbing medicine may be applied to your skin first. Afterwards, the site will be bandaged, and pressure will be applied for at least five minutes to stop bleeding. You may be told to avoid lifting heavy objects for 24 hours after the test.

To get a blood sample from a newborn, a provider will clean the baby's heel with alcohol. Then the provider will stick the baby's heel with a small needle to collect a few drops of blood. The heel will then be bandaged.

Will I need to do anything to prepare for the test?

Your provider will give you specific instructions about how to prepare for an ammonia levels test. You should not smoke for several hours before the test. You may be asked to avoid strenuous exercise and alcohol for a period of time.

You may also need to fast (not eat or drink) for several hours. Your provider may tell you to stop taking certain medicines, including diuretics (water pills) and opioid pain medicines. But never stop taking any prescription medicines without talking with your provider first.

Babies do not need any special preparations before the test.

Are there any risks to the test?

There is very little risk to having a blood test. You may have slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.

If your blood sample was taken from an artery, you may also have some bleeding where the needle was put in. Very rarely, the needle may damage a nerve or the artery.

What do the results mean?

Your provider will use your test results, symptoms, and medical history to understand what your ammonia levels say about your health. Normal levels vary with age, but in general, low levels are normal and healthy.

If your test results are normal, your provider will order other tests to find out what's causing your symptoms.

If your test results show ammonia levels that are higher than normal, it usually means that your body is having trouble getting rid of ammonia. Many types of health conditions can cause high ammonia levels, including:

  • Liver diseases, such as cirrhosis or hepatitis
  • Hepatic encephalopathy
  • Kidney disease or kidney failure
  • Certain genetic disorders, including urea cycle disorders
  • Reye syndrome (most common in in children and teens)
  • Taking certain medicines

If the results of an ammonia levels test are high, more tests will usually be done to diagnose the cause. Treatment will depend on the condition that's causing the problem. If you have questions about your test results or treatment, talk with your provider.

Learn more about laboratory tests, reference ranges, and understanding results.


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The information on this site should not be used as a substitute for professional medical care or advice. Contact a health care provider if you have questions about your health.