Ammonia is a nitrogen-containing compound constantly produced when proteins are broken down into amino acids. This waste product is highly toxic to the nervous system. Therefore, the body must have an efficient mechanism to neutralize and excrete it continuously, maintaining a stable, low concentration in the bloodstream for proper physiological function.
How the Body Handles Ammonia
The majority of ammonia production stems from the metabolic breakdown of amino acids within cells, as well as the action of bacteria in the gut on dietary protein and urea. This ammonia is readily absorbed into the bloodstream and travels via the portal vein directly to the liver. The liver functions as the body’s central detoxification organ for this compound.
Within the liver, the urea cycle efficiently converts toxic ammonia into urea, a far less harmful compound. This process requires multiple enzymes and significant energy. The urea is then released back into the bloodstream, traveling to the kidneys for final filtration and removal through urine. This system operates so effectively that in a healthy individual, ammonia levels remain very low.
Defining a Normal Ammonia Level
The concentration of ammonia considered normal varies based on a person’s age and the specific laboratory performing the test. For adults, the reference range is typically between 15 to 45 micromoles per liter (\(\mu\)mol/L), or 22 to 66 micrograms per deciliter (\(\mu\)g/dL). Children usually have a slightly lower upper limit, but newborns have naturally higher baseline levels, with the upper limit for term infants being around 80 to 90 \(\mu\)mol/L.
These ranges are guidelines, and precise values can differ between testing facilities. Testing for ammonia requires extremely careful handling because the compound’s level increases rapidly after collection. For an accurate measurement, the blood sample must be drawn without delay, placed on ice immediately, and analyzed quickly. Elevated results are not always indicative of disease but can sometimes reflect errors in sample handling or transport.
Health Risks of Elevated Ammonia
When the body’s detoxification system is overwhelmed, ammonia levels rise, a condition termed hyperammonemia. Ammonia is a potent neurotoxin that easily crosses the blood-brain barrier, leading to neurological symptoms. Inside the brain, ammonia converts into glutamine, causing astrocytes—the brain’s support cells—to swell. This cellular swelling leads to cerebral edema, a life-threatening complication.
Symptoms range from subtle changes to severe impairment, depending on the concentration and rate of rise. Early signs include confusion, lethargy, irritability, and changes in sleep patterns. As levels climb, patients may experience slurred speech, tremors, and disorientation. Brain dysfunction caused by liver failure and ammonia buildup is clinically termed hepatic encephalopathy. Severe hyperammonemia can lead to seizures, coma, and death if not promptly managed.
Causes and Management of High Levels
The most frequent cause of elevated ammonia in adults is chronic or acute liver disease, such as cirrhosis or hepatitis. When the liver is damaged, its ability to execute the urea cycle and convert ammonia to urea is compromised, allowing toxins to bypass the liver and enter the systemic circulation. Other factors, like gastrointestinal bleeding or infections, can trigger acute spikes in ammonia levels in people with pre-existing liver issues.
Less common but severe causes include rare genetic defects known as urea cycle disorders, which predominantly affect children. Management focuses on reducing ammonia production and enhancing its removal. Pharmacological treatments include lactulose, a synthetic sugar that traps ammonia in the gut for excretion. Oral antibiotics are also used to reduce ammonia-producing bacteria in the intestines. In acute, severe cases, treatment may involve emergency interventions like hemodialysis to rapidly clear the ammonia from the blood.