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.
Decompensated Cirrhosis
Cirrhosis describes an advanced state of liver scarring resulting 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.
People with decompensated cirrhosis run a high risk for hepatic encephalopathy, also known as portal-systemic encephalopathy. With this condition, chemicals normally detoxified by the liver accumulate in the bloodstream and disrupt normal brain function, explains "The Merck Manual for Healthcare Professionals." Elevated blood ammonia levels are usually a significant contributor to the development of hepatic encephalopathy. Symptoms of this condition include tremors, confusion, sleep disturbances, slurred speech, drowsiness, abnormal eye movements and behavioral disturbances. Patients with hepatic encephalopathy may progress to a comatose state and subsequently die.
Reye's Syndrome
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, reports infectious disease physician Christine S. Ziebold, M.D., Ph.D., M.P.H., of the University of Iowa Children's Hospital. Reye's syndrome causes an acute, severe form of hepatitis, usually accompanied by pronounced liver failure.
An elevated blood ammonia level characteristically occurs in patients with Reye's syndrome, reports the University of Michigan Health System. Brain swelling and ammonia toxicity associated with Reye's syndrome lead to symptoms similar to those seen with hepatic encephalopathy, including irritability, agitation, confusion and drowsiness. Seizures and coma may develop in severe cases.
Gastrointestinal Bleeding
Gastrointestinal bleeding may cause an elevated blood ammonia level, reports the patient information website Lab Tests Online. 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 overwhelm the capacity of the liver to break down the chemical, particularly among patients with pre-existing liver disease.
References
- The Merck Manual for Healthcare Professionals: Portal-Systemic Encephalopathy
- University of Iowa Hospitals and Clinics: September Is Reye's Syndrome Awareness Month
- University of Michigan Health System: Ammonia
- The National Reye's Syndrome Foundation: What Is Reye's Syndrome?
- Lab Tests Online: Ammonia
