What are the other Names for this Test? (Equivalent Terms)
- NH3 Blood Test
What is Ammonia Blood Test? (Background Information)
- Ammonia (NH3) forms in the body, when bacteria in the intestines break-down proteins. It is also produced during breakdown of proteins, by the cells in the body
- NH3 formed in the body is transported to the liver, where it is converted into urea, via a process called urea cycle. This urea is carried to the kidneys, from where it is excreted in urine
- NH3 is toxic to the body and if present in high levels, can lead to a severe condition, called hepatic encephalopathy. Hepatic encephalopathy is a liver condition that can also be caused due to the presence of other toxins in blood
- Ammonia levels in blood can rise as a result of the liver not being able to convert it into urea. The possible causes for this may be liver cirrhosis or severe hepatitis
The Ammonia Blood Test is used to measure ammonia levels in blood. This test can aid in the following:
- Diagnosis of severe liver disease
- Check success of treatment for severe liver disease (i.e. cirrhosis)
- To diagnose certain genetic urea cycle disorders; genetic urea cycle disorders are disorders that result in excess ammonia in blood
- Diagnosis of hepatic encephalopathy
- Diagnosis of Reye syndrome - a childhood disorder that can damage the liver and the brain, which appears to be triggered by a viral illness. Ammonia Testing can aid in predicting the prognosis of an individual diagnosed with Reye syndrome
- To help diagnose kidney failure: If the kidneys are unable to excrete urea, it results in an accumulation of ammonia in blood
- Checking ammonia levels in an individual receiving high-calorie intravenous (IV) nutrition (hyperalimentation)
What are the Clinical Indications for performing the Ammonia Blood Test?
Following are the clinical indications for performing an Ammonia Blood Test:
- The blood test is ordered along with other tests, to investigate causes leading to a change in mental status of an individual, with liver or kidney failure
- The test is also ordered:
- If an adult experiences symptoms, such as confusion, changes in behavior, excessive sleepiness, hand tremor, and coma
- If an infant or child experiences symptoms, such as frequent vomiting, irritability, increased tiredness, respiratory difficulty, and seizures
- If a newborn goes into a coma immediately or about a week after a viral illness, such as an influenza or common cold; this may indicate Reye syndrome
How is the Specimen Collected for Ammonia Blood Test?
Following is the specimen collection process for Ammonia Blood Test:
Sample required: Blood
Process: Insertion of a needle into an arm vein.
Preparation required: Following preparations may be needed depending on the individual’s health circumstances.
- Avoidance of food and drink (except water), or even smoke, for 8 hours prior to the blood test
- Avoidance of strenuous exercise, prior to the test
- Some medications (alcohol, narcotics, valproic acid, diuretics, barbiturates etc.) may increase blood NH3 levels. The healthcare provider should be informed about the use of all medications, prior to the test
What is the Significance of the Ammonia Blood Test Result?
The normal values, called the reference range for ammonia, may vary slightly from lab to lab. Hence, most lab reports come with a reference range, which is used in that particular centre. A physician interprets the results based on the reference values provided.
In general, a standard reference range (normal levels of ammonia in blood) in wide use is:
- Adults: 15-60 mcg/dL (micrograms per deciliter)
- Children: 70-135 mcg/dL
- Newborns: 170-340 mcg/dL
Interpretations of the values are provided:
- An increase in ammonia levels and a decrease in glucose levels are an indicator of the presence of Reye’s syndrome in symptomatic children and adolescents
- In infants, extremely high levels indicate inherited urea cycle disorder, or hemolytic disease of the newborn. ‘Short-lived increases’ are fairly common in newborns, where levels may fluctuate without causing detectible symptoms
- Elevated ammonia levels in children and adults, may indicate liver or kidney damage
- High levels may also be caused by heart failure, or severe bleeding from the stomach/intestines
- Decreased levels are sometimes noted in some forms of hypertension
The laboratory test results are NOT to be interpreted as results of a "stand-alone" test. The test results have to be interpreted after correlating with suitable clinical findings and additional supplemental tests/information. Your healthcare providers will explain the meaning of your tests results, based on the overall clinical scenario.
Additional and Relevant Useful Information:
- Increased levels of ammonia may also be seen with:
- Tourniquet use; the levels may be increased in the blood sample collection
- Muscular exertion - when active, the muscles produce ammonia, which increases blood levels
- Gastrointestinal bleeding - blood cells are hemolyzed in the intestines, releasing protein
- Smoking and the use of specific drugs (such as alcohol, valproic acid, narcotics, diuretics, and barbiturates)
- Severe constipation
- Eating a high-protein or low-protein diet
- Some medications also decrease the level of ammonia. These include antibiotics (neomycin, tetracycline), lactulose, diphendydramine, phenelzine, and tranylcypromine
Certain medications that you may be currently taking may influence the outcome of the test. Hence, it is important to inform your healthcare provider, the complete list of medications (including any herbal supplements) you are currently taking. This will help the healthcare provider interpret your test results more accurately and avoid unnecessary chances of a misdiagnosis.
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References and Information Sources used for the Article:
http://www.nlm.nih.gov/medlineplus/ency/article/003506.htm (accessed on 09/01/2014)
http://labtestsonline.org/understanding/analytes/ammonia/tab/test (accessed on 09/01/2014)
http://www.healthlinkbc.ca/kb/content/medicaltest/hw1768.html#hw1792 (accessed on 09/01/2014)