Ammonia Levels
Reviewed
Also called: NH3 test, blood ammonia test, serum ammonia, ammonia; plasma
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.
Specimen: blood
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 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.
In most cases, a health care professional will take a blood sample from a vein in your arm, using a small needle. 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. 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.
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 (low) ammonia level: in general, low levels are normal and healthy. Limitation: Normal levels vary with age. Next step: If your test results are normal, your provider will order other tests to find out what's causing your symptoms.
- Higher than normal ammonia level (hyperammonemia): 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. Limitation: Even small increases in the level of ammonia in your blood can cause permanent brain damage, coma, and even death. Next step: If the results of an ammonia levels test are high, more tests will usually be done to diagnose the cause.
- 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 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.
- 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
Source: U.S. National Library of Medicine (MedlinePlus). Practices and reference ranges may differ in your country.