| Definition: | A test to measure the amount of ammonium ion in serum (blood).
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| Alternative Names: | NH4+; Ammonia - test
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| How the test is performed: | Adult or child:
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 air-tight 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:
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. Cotton or a bandage may be applied to the puncture site if there is any continued bleeding.
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| 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:
The physical and psychological preparation a parent can provide for this or any test or procedure depends on the child's age, interests, previous experience, and level of trust. For specific information regarding how you can prepare your child, see the following topics as they correspond to your child's age:
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| How the test will feel: | When 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.
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| Why the test is performed: | This test is 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, NH4+ plays a minor role in the acid/base balance but is otherwise a metabolic waste product (primarily the result of proteinmetabolism). 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.
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