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Does this test have other names?

Blood ammonia test, NH3

What is this test?

This test checks the level of ammonia in your blood. It 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 be working 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, and gets rid of it through the liver. It can be added to other chemicals to form an amino acid called glutamine. It can also be used to form 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 any 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 trouble, lower response, 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. This test is done to help find ammonia caused by severe liver disease or kidney failure. You might also have this test if your healthcare provider suspects that you have a rare urea cycle disorder or Reye syndrome. Reye syndrome is 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 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:

  • Liver disease

  • Reye's syndrome

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 arm.

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?

Medicines such as polymyxin B, diuretics, valproic acid and methicillin can cause higher-than-normal results. Other medicines, including tetracycline, lactulose, monoamine oxidase inhibitors, or neomycin, can cause results that are lower than normal.

How do I get ready for this test?

Don';t exercise or smoke cigarettes before this test. 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.

Online Medical Reviewer: Chad Haldeman-Englert MD
Online Medical Reviewer: Heather Trevino
Online Medical Reviewer: Kenny Turley PA-C
Date Last Reviewed: 4/1/2019
© 2000-2021 The StayWell Company, LLC. All rights reserved. This information is not intended as a substitute for professional medical care. Always follow your healthcare professional's instructions.