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Alternative namesNH4+ test
DefinitionThis test is used to measure the amount of ammonium ions in a blood sample.
How the test is performed
Blood is drawn from a vein ( venipuncture ), usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and a tourniquet (an elastic band) or blood pressure cuff is placed around the upper arm to apply pressure and cause veins below the tourniquet to distend (fill with blood).
A needle is inserted into the vein, and the blood is collected in an airtight vial or a syringe. During the procedure, the tourniquet is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding .
Infant or young child:
How to prepare for the test
Fast for 8 to 12 hours. The health care provider may advise you to withhold drugs that may affect test results.
Drugs that can interfere with the test include thiazide or loop diuretics, barbiturates, acetazolamide, neomycin, and oral kanamycin. Consult the health care provider before this test if you are taking any of these medications.
Infants and children:
How the test will feelWhen the needle is inserted to draw blood, some people may feel moderate pain, while others may feel only a prick or stinging sensation. Afterward, there may be some throbbing.
Why the test is performed
This test may be performed when a condition that may cause toxic accumulation of ammonia is present or suspected.
Ammonia (NH4+) is produced by cells throughout the body, especially the intestines, liver, and kidneys. In the kidneys, ammonia plays a minor role in the acid/base balance but is otherwise a metabolic waste product (primarily the result of protein metabolism ).
Most of the ammonia produced in the body is used by the liver in the production of urea. Urea is also a waste product but is much less toxic than ammonia.
Ammonia is especially toxic to the brain and can cause confusion and lethargy and sometimes coma.
The normal range is 15 to 45 mcg/dL.
Note: mcg/dL = micrograms per deciliter
What abnormal results meanConditions that can increase ammonia levels include:
What the risks are
This test is about 90% accurate.
Patients with liver disease may have clotting problems. After the venipuncture , pressure may need to be applied to the puncture site for several minutes to ensure that bleeding has stopped.
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 may be more difficult from some people than from others.
Update Date: 5/20/2003Bridget Martell, M.D., Department of Internal Medicine, Albert Einstein College of Medicine, New York, NY. Review provided by VeriMed Healthcare Network.
Last updated: Tue, 06 Jan 2009 00:20:03 GMT