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Ammonium ion

Ammonium ion

Definition

Ammonium ion test measures the amount of ammonium ions in a blood sample.

Alternative Names

NH4+ test

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, lethargy, and sometimes coma.

How the Test is Performed

Blood is drawn from a vein, usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic. An elastic band is placed around the upper arm to apply pressure and cause the vein to swell with blood.

A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. During the procedure, the band 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.

In infants or young children, the area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. A bandage may be applied to the puncture site if there is any bleeding.

How to Prepare for the Test

Fast for 8 - 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.

How the Test Will Feel

When the needle is inserted to draw blood, you may feel moderate pain, or only a prick or stinging sensation. Afterward, there may be some throbbing.

Risks

  • Excessive bleeding
  • Fainting or feeling light-headed
  • Hematoma (blood accumulating under the skin)
  • Infection (a slight risk any time the skin is broken)
  • Multiple punctures to locate veins

Considerations

This test is about 90% accurate.

Patients with liver disease may have clotting problems. After the venipuncture, pressure should 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.

What Abnormal Results Mean

Conditions that can increase ammonia levels include:

Review Date: 1/17/2007
Reviewed By: Frank A. Greco, M.D., Ph.D., Director, Biophysical Laboratory, The Lahey Clinic, Burlington, MA. Review provided by VeriMed Healthcare Network.
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