Ammonia Levels

Why this test may be ordered

• To help diagnose high ammonia levels in people who have symptoms such as feeling irritable, lack of energy, vomiting, headache, loss of muscle coordination, changes in behavior, confusion, mood swings, or seizures.
• To help diagnose conditions such as hepatic encephalopathy, Reye syndrome, or urea cycle disorders.
• To monitor conditions that cause high ammonia levels and to check if treatment is working.
• 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.

Preparation and collection

Your provider will give you specific instructions. 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.

A health care professional will take a blood sample from a vein in your arm. For newborns, a provider will clean the baby's heel with alcohol and stick it with a small needle to collect a few drops of blood. In certain cases, the blood sample may be taken from an artery in your wrist, arm, or groin.

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.

Understanding results

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.

• Normal: Your ammonia levels are normal. This usually means your body is getting rid of ammonia properly. Limitation: Normal results do not rule out other conditions; your provider will order other tests to find out what's causing your symptoms. Next step: Your provider will order other tests to find out what's causing your symptoms.
• High: Your ammonia levels are higher than normal. This usually means your body is having trouble getting rid of ammonia. Many types of health conditions can cause high ammonia levels, including liver diseases, hepatic encephalopathy, kidney disease or failure, certain genetic disorders (including urea cycle disorders), Reye syndrome, or taking certain medicines. Limitation: High results alone do not diagnose a specific condition; more tests are needed to find the cause. Next step: More tests will usually be done to diagnose the cause. Treatment will depend on the condition that's causing the problem.

• The test alone cannot diagnose conditions that increase the amount of ammonia in your blood.
• 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 to do next

If your test results show ammonia levels that are higher than normal, 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.

• What do my ammonia levels mean in combination with my symptoms and medical history?
• If my results are high, what additional tests might I need to find the cause?
• What treatment options are available for the condition causing high ammonia levels?

Evidence source

U.S. National Library of Medicine: Ammonia Levels