Type of test Blood

Normal findings

 Adult: 10-80 mcg/dL or 6-47 μmol/L (SI units) , Child: 40-80 mcg/dL

Newborn: 90-150 mcg/dL

Test explanation and related physiology

Ammonia is used to support the diagnosis of severe liver diseases (fulminant hepatitis or cirrhosis). Ammonia levels are also used in the diagnosis and follow-up of hepatic encephalopathy.

Ammonia is a byproduct of protein catabolism. Most of the ammonia is made by bacteria acting on proteins present in the gut. By way of the portal vein, ammonia goes to the liver where it is normally converted into urea and then secreted by the kidneys. With severe hepatocellular dysfunction, ammonia cannot be catabolized. Furthermore, when portal blood flow to the liver is altered (e.g., in portal hypertension), ammonia cannot reach the liver to be catabolized. Ammonia levels in the blood rise. Plasma ammonia levels do not correlate well with the degree of hepatic encephalopathy. Inherited deficiencies of urea cycle enzymes, inherited metabolic disorders of organic acids, and the dibasic amino acids lysine and ornithine are major causes of high ammonia levels in infants and adults. Finally, impaired renal function diminishes excretion of ammonia, and blood levels rise. High levels of ammonia are often associated with encephalopathy and coma.

Interfering factors

• Hemolysis increases ammonia levels because the RBCs contain about three times the ammonia content of plasma.

• Muscular exertion can increase ammonia.

 • Cigarette smoking can produce significant increases in levels.

• Ammonia levels may be falsely increased if the tourniquet is too tight for a long period.

*  Drugs that may cause increased ammonia levels include acetazolamide, alcohol, ammonium chloride, barbiturates, diuretics (e.g., loop, thiazide), narcotics, and parenteral nutrition.

* Drugs that may cause decreased levels include broad-spectrum antibiotics (e.g., neomycin), lactobacillus, lactulose, levodopa, and potassium salts.

Procedure and patient care

 • See inside front cover for Routine Blood Testing.

 • Fasting: no

 • Blood tube commonly used: green

• Note that some institutions require that the specimen be sent to the laboratory in an iced container.

• Avoid hemolysis and send the specimen promptly to the laboratory.

• Many patients with liver disease have prolonged clotting times.

Abnormal findings

 Increased levels

- Primary hepatocellular disease

 - Reye syndrome

- Asparagine intoxication

- Portal hypertension

- Severe heart failure with congestive hepatomegaly

- Hemolytic disease of the newborn (erythroblastosis fetalis)

- Gastrointestinal bleeding with mild liver disease

- Gastrointestinal obstruction with mild liver disease

- Hepatic encephalopathy and hepatic coma

- Genetic metabolic disorder of the urea cycle

Decreased levels

- Essential or malignant hypertension

- Hyperornithinemia