Ammonia,Blood

Test Description

Ammonia is a waste product that forms as a result of nitrogen breakdown during                     

intestinal protein metabolism and from digestion of blood which may be in the gastrointestinal

tract (such as from esophageal varices). Another major source of                                              

ammonia is from the synthesis and conversion of glutamine by the renal tubules. In                

the kidneys, ammonia serves as an important renal buffer.                                                         

Normally, ammonia is converted into urea by the liver and then excreted by                            

the kidneys. If a physical disorder prevents this conversion from occurring, the                       

ammonia accumulates in the bloodstream. Toxic levels of ammonia in the blood                     

lead to a problem known as hepatic encephalopathy, in which brain function is                       

affected by the high ammonia levels. Correlation between plasma ammonia and                     

the degree of encephalopathy can be erratic. For example, an individual with very                  

high blood ammonia may show minimal or no effect while another may be greatly                 

affected. The test can be used to determine whether liver dysfunction is the                            

cause of such symptoms as confusion, excessive sleepiness, coma, or hand                             

tremor. It can also be used to monitor the effectiveness of treatment for liver disease,             

such as cirrhosis.

Normal Values

Adult:                                      15–45 mcg/dL (11–32 μmol/L SI units)

Children:                                 40–80 mcg/dL (28–57 μmol/L SI units)

Newborn:                                90–150 mcg/dL (64–107 μmol/L SI units)

Possible Meanings of Abnormal Values

Increased                                                                                 Decreased                  

Acute bronchitis                                                                      Essential hypertension

Azotemia                                                                                 Malignant hypertension

Cirrhosis

Cor pulmonale

Gastrointestinal bleeding

Heart failure

Hemolytic disease of the newborn

Hepatic encephalopathy

Hepatic failure

Hyperalimentation

Leukemia

Pericarditis

Pulmonary emphysema

Renal failure

Reye’s syndrome

Contributing Factors to Abnormal Values

• Drugs that may increase blood ammonia levels: heparin, some diuretics (such as

   furosemide), acetazolamide, and valproic acid.

• Drugs that may decrease blood ammonia levels: neomycin, tetracycline, diphenhydramine,

   isocarboxazid, phenelzine, tranylcypromine, heparin, and lactulose.

• Smoking

• Strenuous exercise

• High-protein or low-protein diet

Interventions/implication

Pretest

• Explain to the patient the purpose of the test and the need for a blood sample to be drawn.

• Instruct the patient to fast for 8 hours before the test. Water is permitted.

• Instruct the patient to avoid strenuous exercise and smoking just prior to the test.

Procedure

• A 5-mL blood sample is collected in an EDTA (lavender-top) tube. The tube should be

  kept on ice.

• Gloves are worn throughout the procedure.

Posttest

• Apply pressure at venipuncture site. Apply dressing, periodically assessing for continued

  bleeding.

• The sample is labeled, placed in ice, and transported to the laboratory immediately.

• Report abnormal results to the health-care provider.

Clinical alert                                                                                                                        

• If the patient is symptomatic of a high ammonia level (such as confusion), treatment

   may include administration of lactulose, a laxative that works by reducing

   ammonia production in the intestines.