Ammonia - blood
The ammonia test measures the amount of ammonia in a blood sample.
How the test is performed
A blood sample is needed. This may be taken from a vein. The procedure is called venipuncture.
How to prepare for the test
You should not eat or drink for 8 - 12 hours before the test. Your doctor may ask you to stop taking certain drugs that can may affect test results.
Drugs that can falsely raise the blood ammonia level include:
- Valproic acid
A high-protein diet can also raise the blood ammonia level. Talk to your health care provider before this test if you are taking any of these medications.
How the test will feel
When the needle is inserted to draw blood, you may feel moderate pain, or only a prick or stinging sensation. Afterward, there may be some throbbing.
Why the test is performed
This test may be done if you have or your doctor thinks you have a condition that may cause a toxic buildup of ammonia. It is most commonly used to diagnose and monitor hepatic encephalopathy, a severe liver disease.
Ammonia (NH3) is produced by cells throughout the body, especially the intestines, liver, and kidneys. Most of the ammonia produced in the body is used by the liver to produce urea. Urea is also a waste product, but it is much less toxic than ammonia.
Ammonia is especially toxic to the brain. It can cause confusion, lethargy, and sometimes coma.
The normal range is 15 - 45 micrograms per deciliter (mcg/dL).
Note: Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.
The examples above show the common results for these tests. Some laboratories use different measurements or may test different samples.
What abnormal results mean
Abnormal results may mean you have increased ammonia levels in your blood. This may be due to:
- Congestive heart failure
- Gastrointestinal (GI) bleeding - usually in the upper GI tract
- Genetic diseases of the urea cycle
- High body temperature (hyperthermia)
- Liver failure
- Low blood potassium level (hypokalemia)
- Metabolic alkalosis
- Severe muscle exertion
What the risks are
Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.
Other risks associated with having blood drawn are slight but may include:
- Excessive bleeding
- Fainting or feeling light-headed
- Hematoma (blood accumulating under the skin)
- Infection (a slight risk any time the skin is broken)
Patients with liver disease may have clotting problems. After the venipuncture, pressure should be applied to the puncture site for several minutes to ensure that bleeding has stopped.
Berk PD, Korenblat KM. Approach to the patient with jaundice or abnormal liver test results. In: Goldman L, Ausiello D, eds. Cecil Medicine. 24th ed. Philadelphia, Pa: Saunders Elsevier; 2011:chap 149.
Nevah MI, Fallon MB. Hepatic encephalopathy, hepatorenal syndrome, hepatopulmonary syndrome, and systemic complications of liver disease. In: Feldman L, Friedman LS, Brandt LJ, eds. Sleisenger and Fordtran's Gastrointestinal and Liver Diseases. 9th ed. Philadelphia, Pa: Saunders Elsevier;2010:chap 92.