Plasma ammonia levels
Why, when, and how to test
-Any unexplained change in consciousness, encephalopathy, and other neurological symptoms should trigger a plasma ammonia test. This is important in people of all ages—but especially in neonates whose clinical history does not match the severity of their illness and/or whose illness is unexplained.
Acute episodes of hyperammonemia can be life-threatening.
Prompt plasma ammonia testing is critical.
Proper procedures for an accurate plasma ammonia test
Lessen the likelihood of inaccurate analysis and—most commonly—false positive results by using proper procedures when conducting plasma ammonia draws. False positive plasma ammonia levels can occur due to many factors.
Refer to FAQs.
The first step in an accurate plasma ammonia test is to alert the laboratory to the incoming STAT order.
Prepare to collect a free-flowing venous or arterial blood sample. Do not use a tourniquet, and keep the patient’s arm as relaxed as possible.
Collect the blood sample in a specimen tube (preferably prechilled) containing either lithium heparin or EDTA as an anticoagulant.
Place the sample on ice. Order the sample to be handled STAT (transported to the lab, separated within 15 minutes of draw, and analyzed immediately).
Call a Metabolic Geneticist
Call a metabolic geneticist immediately to evaluate any signs or symptoms that may suggest an inborn error of metabolism (IEM).
Individual inborn errors of metabolism (IEMs) are rare, but collectively the disorders are common.
Expected turn-around time for lab results is <1 hour.
Do not wait for test results to call a metabolic geneticist.
Download Testing for Hyperammonemia – The Essentials Brochure
This downloadable brochure is designed for lab technicians, nurses, and other allied healthcare professionals. It explains blood draw procedures, analysis of the results, and additional testing that may be done to differentiate among the causes of hyperammonemia.
Analysis of Plasma Ammonia Test Results
(Normal, Age-Dependent Blood Ammonia Reference Levels – Association of Clinical Biochemistry*)
Premature neonates:
< 150 μmol/L
Term neonates:
< 100 μmol/L
Infants:
< 40 μmol/L
Adults:
11-32 μmol/L
*Individual laboratory reference levels may vary.