When someone with or without liver disease or kidney failure experiences mental changes or lapses into a coma; when a newborn experiences frequent vomiting and increased lethargy or when a child has continuous vomiting and unusual sleepiness during recovery from a viral illness, such as the flu or chickenpox
A blood sample drawn from a vein
Ammonia is a waste product formed primarily by bacteria in the intestines during the digestion of protein. If not processed and cleared from the body appropriately, excess ammonia can accumulate in the blood. This test measures the amount of ammonia in the blood.
Ammonia is normally transported in the blood to the liver, where it is converted into two substances called urea and glutamine. The urea is then carried to the kidneys, where it is eliminated in the urine. If this "urea cycle" does not complete the breakdown of ammonia, ammonia builds up in the blood and can pass from the blood into the brain.
Ammonia is toxic to the brain. For example, when liver function is significantly reduced due to disorders such as cirrhosis or hepatitis, ammonia and other compounds processed by the liver can accumulate in the brain and cause a condition called hepatic encephalopathy.
Hepatic encephalopathy causes mental and neurological changes that can lead to confusion, disorientation, sleepiness, and eventually to coma and even death.
Infants and children with increased ammonia levels may vomit frequently, be irritable, and be increasingly lethargic. Left untreated, they may experience seizures, have difficulty breathing, and may lapse into a coma.
Problems with ammonia processing can arise from conditions such as:
- Severe liver disease – damage limits the ability of the liver to process ammonia; spikes in ammonia blood levels may be seen in people with stable liver disease, especially following a triggering event such as gastrointestinal bleeding or an electrolyte imbalance.
- Decreased blood flow to the liver – ammonia is less able to get to the liver to be processed.
- Reye syndrome – a rare condition that affects the blood, brain, and liver; it typically causes a rise in ammonia levels and a fall in glucose. It affects primarily children and young adults. In most cases, it follows and appears to be triggered by a viral infection, such as the flu or chickenpox. Children who are given aspirin are at an increased risk.
- Kidney (renal) failure – the kidneys are unable to effectively rid the body of urea, leading to a build-up of ammonia in the blood.
- Rare genetic disorder such as a defect in the urea cycle – a deficiency in one of the enzymes necessary to complete the conversion of ammonia to urea.
How is the test used?
The ammonia test is used to detect an elevated level in the blood. It may be ordered, along with other tests such as glucose, electrolytes, and kidney and liver function tests, to investigate the cause of changes in your behavior and consciousness or to help support the diagnosis of Reye syndrome or hepatic encephalopathy caused by various liver diseases.
Some healthcare practitioners use the ammonia test to monitor the effectiveness of treatment of hepatic encephalopathy, but there is not widespread agreement on this use. Since hepatic encephalopathy can be caused by the build-up of a variety of toxins in the blood and brain, blood ammonia levels correlate poorly with the severity of the condition.
An ammonia level may also be ordered to help diagnose certain rare genetic disorders. For example, it may be used to diagnose a urea cycle defect, to evaluate the severity of the urea cycle impairment in this condition, and also to monitor treatment.
For more on Reye syndrome, hepatic encephalopathy, and urea cycle disorders, see the links in the Related Content section below.
When is it ordered?
- Mental changes, disorientation
- Change in consciousness
The above symptoms can occur with and without liver disease or kidney failure. In you have stable liver disease, an ammonia level may be ordered, along with other liver function tests, when you suddenly become acutely ill.
An ammonia test may be ordered when a newborn has signs and symptoms that arise in the first few days after birth, such as:
What does the test result mean?
A significantly increased level of ammonia in the blood indicates that your body is not effectively processing and eliminating ammonia and it may be the cause of your signs and symptoms.
In children and adults, an elevated ammonia level may indicate that severe liver or kidney damage has affected the body's ability to clear ammonia and that the brain may be affected. Frequently, an acute or chronic illness will act as a trigger, increasing ammonia levels to the point that an affected person has difficulty clearing the ammonia.
In infants, high levels might indicate impairment of the urea cycle due to a rare genetic disorder such as a deficiency of one of the urea cycle enzymes, or may also be seen with hemolytic disease of the newborn. Moderate, temporary increases in ammonia are relatively common in newborns, where the level may rise and fall without causing noticeable symptoms. (For more about urea cycle disorders, see the links in the Related Content section below.)
An increased ammonia and low glucose in combination with elevated levels of certain liver enzymes may indicate the presence of Reye syndrome in symptomatic children and teens. An increased level may also indicate a previously undiagnosed enzymatic defect of the urea cycle.
A normal blood ammonia level may mean that your signs and symptoms are due to a cause other than excess ammonia. However, normal levels of ammonia do not rule out hepatic encephalopathy. Other breakdown products can contribute to changes in mental function and consciousness, and brain levels of ammonia may be much higher than blood levels. This can make correlation of symptoms to ammonia blood levels difficult.
A decreased level of ammonia may be seen with some types of hypertension, such as essential (high blood pressure of unknown cause) and malignant (very high blood pressure that occurs suddenly and quickly).
Is there anything else I should know?
Increased levels of ammonia may also be seen with:
- Gastrointestinal bleeding – blood cells are hemolyzed in the intestines, releasing protein.
- Muscular exertion – muscles produce ammonia when active and absorb it when resting.
- Tourniquet use – ammonia levels can be increased in the blood sample collected.
- High protein intake – high protein diet might trigger ammonia accumulation in some patients.
- Prematurity – in rare cases, very high ammonia levels can be seen in premature babies with respiratory distress.
- Use of certain drugs, including alcohol, barbiturates, diuretics, high-dose chemotherapy, valproic acid, and narcotics
- Cigarette smoking
Decreased levels of ammonia may be seen with the use of some antibiotics, such as neomycin and metronidazole.
Ammonia tests can also be performed on blood from an artery, but this is much less common than using blood from a vein. Some healthcare practitioners feel that arterial ammonia measurements are more clinically useful, but there is not widespread agreement on this.
Is ammonia testing used to detect or monitor ammonia poisoning?
Not generally. In most cases, ammonia acts locally, burning or irritating whatever it comes in contact with, but according to the Agency for Toxic Substances and Disease Registry (ATSDR), it does not usually act as a systemic poison. Concentrated commercial ammonia, in a liquid or vapor form, can cause more severe burns than the more dilute liquid household ammonia, but both can damage the eyes, skin, respiratory tract, and, if swallowed, the mouth, throat, and stomach.
When my increased ammonia level has returned to normal, can it rise again?
It depends on why it was increased in the first place. If you had a temporary condition, then it is likely that the ammonia level will continue to be normal. If you have a chronic condition, then it is possible that it will increase again and your health status will likely need to be monitored. Talk to your healthcare provider about what is best for you.