Top of the page
An ammonia test measures the amount of ammonia in the blood. Most ammonia in the body forms when protein is broken down by bacteria in the intestines. The liver normally converts ammonia into urea, which is then eliminated in urine.
Ammonia levels in the blood rise when the liver is not able to convert ammonia to urea. This may be caused by cirrhosis or severe hepatitis.
For this test, a blood sample may be taken from either a vein or an artery.
An ammonia test is done to:
Do not eat, drink anything other than water, or smoke for 8 hours before having an ammonia blood test.
Avoid strenuous exercise just prior to having this test.
Tell your doctor if you:
Talk to your doctor about any concerns you have regarding the need for the test, its risks, how it will be done, or what the results may mean. To help you understand the importance of this test, fill out the medical test information form .
The health professional taking a sample of your blood will:
A sample of blood from an artery is usually taken from the inside of the wrist (radial artery), but it can also be taken from an artery in the groin (femoral artery) or on the inside of the arm above the elbow crease (brachial artery). You will be seated with your arm extended and your wrist resting on a small pillow. The health professional drawing the blood may rotate your hand back and forth and feel for a pulse in your wrist.
To prevent the chance of damaging the artery of the wrist when the blood sample is taken, a procedure called the Allen test may be done to make sure that blood flow to your hand is normal. An ammonia test will not be done on an arm used for dialysis or if there is an infection or inflammation in the area of the puncture site.
The blood sample is taken from a vein in your arm. An elastic band is wrapped around your upper arm. It may feel tight. You may feel nothing at all from the needle, or you may feel a quick sting or pinch.
Collecting blood from an artery is more painful than collecting it from a vein because the arteries are deeper and are protected by nerves.
There is very little chance of a problem from having a blood sample taken from a vein.
There is little chance of a problem from having a blood sample taken from an artery.
Though problems are rare, be careful with the arm or leg that had the blood draw. Do not lift or carry objects for about 24 hours after you have had blood drawn from an artery.
An ammonia test measures the amount of ammonia in the blood. Results are usually available within 12 hours.
The normal values listed here—called a reference range—are just a guide. These ranges vary from lab to lab, and your lab may have a different range for what's normal. Your lab report should contain the range your lab uses. Also, your doctor will evaluate your results based on your health and other factors. This means that a value that falls outside the normal values listed here may still be normal for you or your lab.
9.5–49 micrograms per decilitre (mcg/dL)
7–35 micromoles per litre (mcmol/L)
High levels of ammonia in the blood may be caused by:
High ammonia values in a baby may be present when the blood types of a mother and her baby do not match (hemolytic disease of the newborn).
Reasons you may not be able to have the test or why the results may not be helpful include:
CitationsChernecky CC, Berger BJ (2013). Laboratory Tests and Diagnostic Procedures, 6th ed. St. Louis: Saunders.Other Works ConsultedChernecky CC, Berger BJ (2013). Laboratory Tests and Diagnostic Procedures, 6th ed. St. Louis: Saunders.Fischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.Pagana KD, Pagana TJ (2010). Mosby's Manual of Diagnostic and Laboratory Tests, 4th ed. St. Louis: Mosby.
Current as of: September 23, 2020
Author: Healthwise StaffMedical Review: E. Gregory Thompson MD - Internal MedicineAnne C. Poinier MD - Internal MedicineAdam Husney MD - Family MedicineMartin J. Gabica MD - Family MedicineJerome B. Simon MD, FRCPC, FACP - Gastroenterology
Current as of: September 23, 2020
Author: Healthwise Staff
Medical Review:E. Gregory Thompson MD - Internal Medicine & Anne C. Poinier MD - Internal Medicine & Adam Husney MD - Family Medicine & Martin J. Gabica MD - Family Medicine & Jerome B. Simon MD, FRCPC, FACP - Gastroenterology
To learn more about Healthwise, visit Healthwise.org.
© 1995-2021 Healthwise, Incorporated. Healthwise, Healthwise for every health decision, and the Healthwise logo are trademarks of Healthwise, Incorporated.