Plasma ammonia levels Why, when, and how to test

Any unexplained change in consciousness, encephalopathy, and with other neurological symptoms should trigger a plasma ammonia test.1 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.2

Acute episodes of hyperammonemia can be life threatening.1
Prompt plasma ammonia testing is critical.1

Download the FAQ

Learn more about plasma ammonia testing.

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.2,3 False positive plasma ammonia levels can occur due to many factors.
Refer to FAQs.

Follow these steps to ensure an accurate plasma ammonia result:

  1. Alert the laboratory to
    the incoming STAT order.2
  2. 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.4,5,6
  3. Collect the blood sample in a specimen tube (preferably prechilled) containing either lithium heparin or EDTA as an anticoagulant.4
  4. 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).4

Accurate lab results are critical and depend on proper sampling technique and immediate transport. Watch this short video with helpful tips to ensure an accurate plasma ammonia test result.

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.7,9
Expected turn-around time for lab results is <1 hour.1 Do not wait for test results to call a metabolic geneticist.1,8

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*)3

Premature neonates:
< 150 μmol/L

Term neonates:
< 100 μmol/L

< 40 μmol/L

11-32 μmol/L

*Individual laboratory reference levels may vary.


1. Haberle J. Clinical practice: The management of hyperammonemia. Eur J Pediatr 2011;170:21-34.

2. Broomfield A, Grunewald S. How to use serum ammonia. Arch Dis Child Educ Pract Ed 2012;97:72–77

3. Ammonia. Lab Tests Online. American Association for Clinical Chemistry (AACC). February 29, 2016. Available at: Accessed September 11, 2017.

4. Hawke L. Ammonia (plasma, blood). The Association for Clinical Biochemistry and Laboratory Medicine. Available at: Published 2012. Accessed September 7, 2017.

5. Barsotti RJ. Measurement of ammonia in blood. J Pediatr 2001;138(1):S11-S20.

6. Orton DJ, Gifford JL, Seiden-Long I, Khan A, de Koning L. Critically high plasma ammonia in an adolescent girl. Clin Chem 2016;62(12):1565-1569.

7. Gupta A. To err is genetics: Diagnosis and management of inborn errors of metabolism (IEM). Chapter 32, pp. 415-423. In Anthropology Today: Trends, Scope and Applications. Eds. V Bhasin & MK Basin. New Delhi, India: Kamla-Raj Enterprises, 2007. Anthropologist Special Volume No. 3 2007:415-423.

8. Blair NF, Cremer PD, Tchan MC. Urea cycle disorders: a life-threatening yet treatable cause of metabolic encephalopathy in adults. Pract Neurol 2015;15:45-48.

9. Inherited metabolic disorders. Most recent review: October 20, 2016. Available at: Accessed September 11, 2017.