Blood ammonia comes primarily from the bacterial breakdown of unabsorbed dietary protein in the intestine. Intestinal ammonia passes into the bloodstream and travels to the liver, which converts ammonia into urea. Urea subsequently passes from the body through the urine. High blood ammonia levels can occur with various forms of chronic liver disease, acute liver failure and gastrointestinal bleeding. Elevated blood ammonia levels adversely affect brain function. Early diagnosis and treatment of an elevated blood ammonia level helps reduce the risk of potentially life-threatening complications.
Cirrhosis -- advanced liver scarring -- results from long-standing, chronic liver disease. In the early stages of cirrhosis, the liver often continues to perform its numerous functions. With advanced cirrhosis, however, liver failure develops and gradually progresses. This condition, known as decompensated cirrhosis, leads to increasingly severe metabolic and chemical disturbances in the body.
Chemicals normally detoxified by the liver accumulate in the bloodstream and disrupt normal brain function, causing anxiety, decreased attention, depression and bipolar disorder. High blood ammonia levels may also cause tremors, confusion, sleep disturbances, slurred speech, drowsiness, abnormal eye movements and behavioral disturbances.
Reye's syndrome is a rare condition primarily affecting the liver and brain. The disorder most commonly develops in children ages 5 to 14 after an otherwise unremarkable viral illness. An elevated blood ammonia level characteristically occurs in patients with Reye's syndrome. Brain swelling and ammonia toxicity associated with Reye's syndrome can cause irritability, agitation, confusion and drowsiness. Seizures and coma may develop in severe cases.
Gastrointestinal bleeding may cause an elevated blood ammonia level. Red blood cells contain a high concentration of protein. Significant bleeding, especially in the upper part of the digestive system, increases the protein load in the intestine and the production of ammonia. The increased ammonia from the intestine may make it difficult for the liver to break down the chemical, particularly if you have pre-existing liver disease.
- BMC Gastroenterology: A Capillary Blood Ammonia Bedside Test Following Glutamine Load to Improve the Diagnosis of Hepatic Encephalopathy in Cirrhosis
- BMC Gastroenterology: Blood Ammonia Levels in Liver Cirrhosis -- A Clue for the Presence of Portosystemic Collateral Veins
- The National Reye's Syndrome Foundation: What Is Reye's Syndrome?
Dr. Tina M. St. John owns and operates a health communications and consulting firm. She is also an accomplished medical writer and editor, and was formerly a senior medical officer with the U.S. Centers for Disease Control and Prevention. St. John holds an M.D. from Emory University School of Medicine.