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What Are the Causes of High Blood Ammonia Level?

author image Dr. Tina M. St. John
Tina M. St. John runs a health communications and consulting firm. She is also an author 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.
What Are the Causes of High Blood Ammonia Level?
Smoking and certain medications can cause a temporary increase in blood ammonia. Photo Credit Hemera Technologies/Photos.com/Getty Images


Ammonia is produced as a byproduct of bacterial breakdown of unabsorbed dietary protein in the intestine, and protein breakdown elsewhere in the body. The kidneys also produce ammonia as part of their role in maintaining a normal body pH. Ammonia enters the bloodstream and travels to the liver, which converts it into urea. Urea subsequently passes from the body through the urine. High blood ammonia levels most frequently occur because of severe liver disease. Other possible causes include gastrointestinal bleeding, Reye syndrome, metabolic diseases, urinary tract disorders and certain medications, among others. Elevated blood ammonia adversely affects the brain. Early diagnosis and treatment of an elevated blood ammonia level reduces the risk of potentially life-threatening complications.

Decompensated Cirrhosis

Cirrhosis -- advanced liver scarring -- results from long-standing, chronic liver disease. In the early stages of cirrhosis, the liver continues to perform its numerous functions relatively normally. 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. Ammonia and other chemicals normally detoxified by the liver accumulate in the bloodstream and frequently disrupt normal brain function, causing anxiety, decreased attention, depression and other mental symptoms. High blood ammonia levels may also cause tremors, confusion, sleep disturbances, slurred speech, drowsiness, abnormal eye movements and behavioral disturbances.

Gastrointestinal Bleeding

Heavy bleeding in the gastrointestinal tract 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 overwhelm the liver's capacity to break down the chemical, leading to an elevated blood ammonia level. People with preexisting liver disease are particularly susceptible to this scenario due to their already compromised liver function.

Urinary Tract Disorders

As the kidneys generate a significant amount ammonia, some urinary tract disorders can potentially lead to an elevated blood ammonia level. For example, urinary tract infections caused by bacteria capable of breaking down urea into ammonia can lead to a high blood ammonia level. An abnormal connection between the bladder and rectum that allows urine to drain into the rectum can increase blood ammonia levels by a similar bacterial mechanism. People who have undergone urinary diversion surgery -- a procedure in which the urine from the kidneys is diverted into a holding pouch constructed of a segment of the bowel -- can also experience an elevated ammonia level due to absorption of the chemical from the holding pouch into the bloodstream. This type of surgery is most often performed when the bladder must be removed, usually due to cancer.

Reye Syndrome

Reye 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. Deranged liver function with Reye syndrome leads to an elevated blood ammonia level. Brain swelling and ammonia toxicity associated with Reye syndrome can cause a variety of symptoms including nausea, vomiting, weakness, hearing changes, vision changes, memory loss, irritability, agitation, confusion and extreme drowsiness. Symptoms can progress rapidly, leading to seizures and coma in severe cases.

Other Causes

High blood ammonia levels characteristically occur with certain genetic metabolic disorders that interfere with the body's normal processing of protein and/or urea. These conditions usually manifest shortly after birth, although milder disorders might not be apparent until later in childhood or even adulthood, in rare cases. Certain medications can also cause an elevated blood ammonia level, including some chemotherapy drugs and overdoses of some antiseizure medications. Any medical condition that leads shock can also cause an elevated blood ammonia level due to a combination of mechanisms.

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