Alternative names
NH4+ test

Definition
This 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:
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.

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:

 
• Infant test or procedure preparation (birth to 1 year)  
• Toddler test or procedure preparation (1 to 3 years)  
• Preschooler test or procedure preparation (3 to 6 years)  
• School age test or procedure preparation (6 to 12 years)  
• Adolescent test or procedure preparation (12 to 18 years)

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.

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.

Normal Values

The normal range is 15 to 45 mcg/dL.

Note: mcg/dL = micrograms per deciliter

What abnormal results mean

Conditions that can increase ammonia levels include:

 
• Liver failure  
• Severe Congestive heart failure  
• Erythroblastosis fetalis  
• Gastrointestinal (GI) bleeding - usually in the upper GI tract  
• Ggenetic diseases of the urea cycle  
• Leukemia  
• Pericarditis  
• Reye’s syndrome  
• Certain drugs

What the risks are

 
• 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

Special considerations

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.

Medical Encyclopedia

All ArmMed Media material is provided for information only and is neither advice nor a substitute for proper medical care. Consult a qualified healthcare professional who understands your particular history for individual concerns.