Does this test have other names?
Blood ammonia test, NH3
What is this test?
This test checks the level of ammonia in your blood. The test helps find out why you
may have changes in consciousness and also helps diagnose a liver disease called hepatic
encephalopathy. This disease affects how your brain works, because of excess toxins,
or poisons, in your body.
Your liver may not work properly if you have high levels of ammonia in your blood.
Ammonia is a chemical made by bacteria in your intestines and your body's cells while
you process protein. Your body treats ammonia as a waste product. It turns it into
an amino acid called glutamine and a chemical compound called urea. Your bloodstream
moves the urea to your kidneys, where it is eliminated in your urine.
But ammonia will build up in your body if you can't get rid of urea. This can sometimes
happen if you have kidney or liver failure. It can also happen if you have a urea
cycle disorder, a genetic disorder that means your body is missing one of the enzymes
that remove ammonia from the blood. The ammonia blood test is the gold standard for
diagnosing urea cycle disorders.
Too much ammonia in your body can cause psychological problems like confusion, tiredness,
and possibly coma or death.
A child's reaction to too much ammonia can include seizures, breathing difficulties,
and potentially death.
Why do I need this test?
You might have this test if you have abnormal neurological changes or you enter a
coma unexpectedly. You might also have this test if your healthcare provider suspects
that you have a urea cycle disorder or Reye's syndrome, a potentially fatal disease
that affects the brain and liver. Children may have this test if they frequently vomit
or are very tired within a week after a virus-related illness.
What other tests might I have along with this test?
If your healthcare provider suspects that you have a urea cycle disorder, he or she
may order other tests that look at ammonia levels in your body.
What do my test results mean?
Many things may affect your lab test results. These include the method each lab uses
to do the test. Even if your test results are different from the normal value, you
may not have a problem. To learn what the results mean for you, talk with your healthcare
Test results are given in micrograms per deciliter (mcg/dL).
Normal ranges are:
Age 0 to 10 days (enzymatic): 170 to 341 mcg/dL
Infants and toddlers, from 10 days to 2 years old (enzymatic): 68 to 136 mcg/dL
Children, older than 2 years (enzymatic): 19 to 60 mcg/dL
Adults: 10 to 80 mcg/dL
If your test results are higher than normal, it can mean that you have:
People who have a portacaval shunt in their liver to treat high blood pressure may
also have higher levels of ammonia.
Levels that are lower than normal can mean that your kidneys aren't removing waste
as they should.
How is this test done?
The test requires a blood sample, which is drawn through a needle from a vein in your
Does this test pose any risks?
Taking a blood sample with a needle carries risks that include bleeding, infection,
bruising, or feeling dizzy. When the needle pricks your arm, you may feel a slight
stinging sensation or pain. Afterward, the site may be slightly sore.
What might affect my test results?
Medications such as polymyxin B, diuretics, valproic acid and methicillin can cause
higher-than-normal results. Other medications, including tetracycline, lactulose,
monoamine oxidase inhibitors, or neomycin, can cause results that are lower than normal.
How do I get ready for this test?
You should avoid exercising or smoking cigarettes before this test, but no other preparation
is needed. Be sure your healthcare provider knows about all medicines, herbs, vitamins,
and supplements you are taking. This includes medicines that don't need a prescription
and any illicit drugs you may use.