Blood ammonia comes from two sources: (1) deamination of amino acids during protein metabolism and (2) degradation of proteins by colon bacteria. The liver converts ammonia to urea, generating glutamine as an intermediary. The kidneys then use glutamine as a source for synthesizing ammonia for renal regulation of electrolyte and acid-base balance. Serum ammonia levels have little effect on renal excretion of ammonia.

Circulating blood normally contains very little ammonia because the liver converts ammonia in the portal blood to urea. When liver function is severely compromised, especially in situations when decreased hepatocellular function is combined with impaired portal blood flow, ammonia levels rise. Both elevated serum ammonia and abnormal glutamine metabolism have been implicated as etiologic factors in hepatic encephalopathy (hepatic coma).²¹ Additional causes of altered serum ammonia levels are listed in Table 5-8.

• Evaluation of advanced liver disease or other disorders associated with altered serum ammonia levels (see Table 5-8)
• Identification of impending hepatic encephalopathy in clients with known liver diseases (e.g., after bleeding from esophageal varices or other gastrointestinal sources, or after excessive ingestion of protein) as indicated by rising levels
• Monitoring for the effectiveness of treatment for hepatic encephalopathy as indicated by declining levels

Nursing Care Before the Procedure

Client preparation is essentially the same as that for any study involving the collection of a peripheral blood sample (see Appendix I). An 8-hour fast from food is required before the test.

A venipuncture is performed and the sample collected in a green-topped tube. Some laboratories require that the sample be placed in ice immediately on collection. The sample should be handled gently to avoid hemolysis and sent promptly to the laboratory.

Nursing Care After the Procedure

Care and assessment after the procedure are the same as for any study involving the collection of a peripheral blood sample. Resume foods withheld before the test.