Blood ammonia 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.
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 doctor 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.
If your doctor suspects that you have a urea cycle disorder, he or she may order other tests that look at ammonia levels in your body.
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 health care provider.
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.
The test requires a blood sample, which is drawn through a needle from a vein in your arm.
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.
Medications such as polymyxin B, diuretics, and methicillin can cause higher-than-normal results. Other medications, including tetracycline, lactulose, or neomycin, can cause results that are lower than normal.
You should avoid exercising before this test, but no other preparation is needed. Be sure your doctor 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.