Ammonia test

A blood sample will be taken from a vein or artery in your arm. 

You should avoid smoking cigarettes before the test as smoking can increase ammonia levels. 

The sample must be sent to the laboratory very quickly for analysis because ammonia levels can change rapidly in blood samples. 

What the test measures 

Ammonia is a poisonous waste product made in your body in two ways: – by bacteria in your intestines and by your cells when they break down proteins. 

Normally, this ammonia is transported to your liver where it’s converted into two safer chemicals – urea and glutamine. The urea then travels in your blood to your kidneys, where it’s removed in urine. 

If this system doesn’t work properly, ammonia builds up in your blood and passes into your brain, where it’s extremely toxic. This can cause serious brain damage. 

Hepatic encephalopathy 

When ammonia and other toxic compounds normally broken down by the liver accumulate, they can cause a condition called hepatic encephalopathy. This is a brain disorder caused by liver failure. 

Symptoms include: 

• Confusion 
• Disorientation 
• Drowsiness 
• Eventually coma and death if untreated 
• In infants and children: vomiting, irritability, extreme tiredness, seizures, breathing difficulty 

What causes ammonia build-up 

Several conditions can cause ammonia to accumulate: 

• Severe liver disease: the damaged liver can’t break down and remove ammonia effectively. Sudden spikes may occur after bleeding in the stomach or intestines, or electrolyte imbalances 
• Urea cycle defects: rare inherited genetic conditions where you lack one or more enzymes needed to convert ammonia to urea. These typically (but not always) appear in newborns 
• Reduced blood flow to the liver: less ammonia can be removed 
• Reye’s syndrome: a rapidly developing condition affecting the blood, brain, and liver. Usually follows a viral infection in children and young adults. Risk is increased by aspirin use. Causes high ammonia and low glucose 
• Kidney failure: kidneys can’t effectively remove urea, leading to ammonia build-up 

What your results mean 

Significantly raised ammonia 

Very high ammonia levels indicate your body isn’t effectively breaking down and/​or removing ammonia. However, the results don’t explain why this is happening – further tests are needed to identify the cause. 

In newborns, extremely high ammonia can indicate: 

• Inherited urea cycle enzyme deficiency (most common cause) 
• Haemolytic disease of the newborn (a condition where the baby’s red blood cells are destroyed) 

Short-lived increases in ammonia are relatively common in newborns and may rise and fall without causing noticeable symptoms. 

In children and adolescents with symptoms after a viral illness: 

Increased ammonia plus decreased glucose suggests Reye’s syndrome. 

Raised ammonia may also suggest a previously undiagnosed urea cycle defect. 

In children and adults, raised ammonia can indicate: 

• Liver damage 
• Kidney damage 

Normal ammonia 

Normal ammonia levels don’t rule out hepatic encephalopathy. Other toxic waste products also contribute to brain dysfunction, and brain ammonia levels may be much higher than blood levels. 

Patients with severe symptoms don’t always have very high blood ammonia levels.

If ammonia is raised 

Further tests to identify the cause: 

• Liver function tests 
• Kidney function tests 
• Glucose test 
• Electrolytes 
• Blood gas tests 
• Genetic testing for urea cycle defects (if suspected) 
• Imaging (ultrasound, CT scan of liver) 

Emergency treatment: 

High ammonia levels require urgent treatment to prevent brain damage. Treatment focuses on reducing ammonia production and removing ammonia from the blood. 

• Reduce ammonia production: lactulose (a laxative that reduces ammonia-producing bacteria in intestines), antibiotics like rifaximin, low-protein diet 
• Remove ammonia: medications that help convert ammonia to compounds that can be excreted, or dialysis in severe cases 
• Treat underlying cause: stopping bleeding if present, correcting electrolyte imbalances, treating liver or kidney disease 
• Liver transplant: may be needed for severe liver disease or some urea cycle defects 

Monitoring treatment 

Some doctors use ammonia tests to monitor treatment effectiveness in hepatic encephalopathy, though there’s no widespread agreement on how useful this is. Ammonia levels don’t always correlate well with symptom severity because other toxic substances also contribute to brain dysfunction. 

If ammonia levels return to normal from a temporary condition, they’re likely to stay normal. If the underlying condition is chronic (long-lasting), levels may rise again and ongoing monitoring may be needed. 

Factors that can increase ammonia levels: 

• Gastrointestinal bleeding: blood cells break apart in intestines, releasing protein that’s digested and converted to ammonia 
• Muscle exercise: muscles produce ammonia when active (they absorb it when resting) 
• Smoking: cigarettes increase ammonia 
• Prolonged tourniquet use: when taking the blood sample 
• Medications: alcohol, barbiturates, diuretics, valproic acid, narcotics 

Factors that can decrease ammonia levels: 

• High blood pressure 
• Some antibiotics (like neomycin)

Ammonia testing is almost always done alongside other tests to identify the cause and assess severity. 

Liver tests: 

• ALT (alanine aminotransferase) 
• AST (aspartate aminotransferase) 
• ALP (alkaline phosphatase) 
• Bilirubin 
• Albumin 

Kidney tests: 

• Urea 
• Creatinine 
• eGFR (estimated glomerular filtration rate) 

Other tests: 

• Glucose (low in Reye’s syndrome) 
• Electrolytes (sodium, potassium, chloride) 
• Blood gas tests 
• Genetic testing (for urea cycle defects) 
• Imaging (ultrasound, CT scan of liver) 

Ammonia is extremely toxic to the brain. Even small increases can cause problems with thinking and consciousness. The brain is particularly vulnerable because ammonia interferes with normal brain cell function and energy production. 

In hepatic encephalopathy, ammonia is just one of several toxic substances that build up when the liver fails. Others include manganese, mercaptans, and false neurotransmitters. This is why blood ammonia levels don’t always match symptom severity – all these toxins work together to affect the brain. 

The severity of hepatic encephalopathy is graded from 1 to 4. Grade 1 involves mild confusion and changes in sleep patterns. Grade 4 is coma. Treatment becomes more urgent as the grade increases. 

This test is not used to detect environmental ammonia poisoning. Commercial ammonia (in cleaning products) acts locally, causing burns to the eyes, skin, respiratory tract, or digestive tract if swallowed. It doesn’t usually poison the whole body in the way that high blood ammonia does.