Ammonia
Also known as: Blood Ammonia, NH3
What Does Ammonia Measure?
Blood ammonia (NH3) measures the level of ammonia circulating in your bloodstream. Ammonia is a nitrogen-containing waste product that forms primarily when bacteria in your intestines break down dietary protein, and when your body's cells break down amino acids for energy. Under normal circumstances, ammonia is rapidly transported to the liver, where it is converted into urea through a process called the urea cycle, and then safely excreted by the kidneys in urine.
Why Does Ammonia Matter?
Ammonia levels are a critical indicator of liver function because the liver is the primary organ responsible for detoxifying this potentially harmful compound. When the liver is damaged or blood flow is bypassed around it, ammonia accumulates in the bloodstream and can cross the blood-brain barrier, causing a serious neurological condition called hepatic encephalopathy — characterized by confusion, disorientation, tremors, and in severe cases, coma. Ammonia testing is also essential in diagnosing inherited urea cycle disorders in newborns and children, as well as monitoring patients with cirrhosis, acute liver failure, or those receiving certain medications like valproic acid.
Normal Ranges
Males
15–45 mcg/dL (11–32 µmol/L)
Females
15–45 mcg/dL (11–32 µmol/L)
Children
Varies by age; newborns: 90–150 mcg/dL; infants: 40–80 mcg/dL; older children: 20–50 mcg/dL
Causes of High Levels
- Liver cirrhosis or severe liver disease impairing the urea cycle
- Acute liver failure from viral hepatitis, drug toxicity, or ischemia
- Portosystemic shunting where blood bypasses the liver
- Inherited urea cycle enzyme deficiencies (e.g., ornithine transcarbamylase deficiency)
- Gastrointestinal bleeding, which increases protein load in the gut for bacterial breakdown
- Reye's syndrome, a rare condition affecting children after viral illness and aspirin use
- High-protein diet combined with impaired liver or kidney function
- Valproic acid or other medications that interfere with the urea cycle
Causes of Low Levels
- Hyper-hydration or excessive fluid intake diluting ammonia concentration
How to Improve Your Ammonia
Diet
- Reduce but do not eliminate dietary protein; aim for 1.0–1.2 g/kg body weight per day from high-quality sources like eggs and dairy
- Prefer plant-based proteins (legumes, nuts, seeds) over red meat, as they produce less ammonia during digestion
- Eat small, frequent meals throughout the day to avoid overwhelming the liver's detoxification capacity
- Increase dietary fiber intake through vegetables, fruits, and whole grains to promote faster gut transit and reduce bacterial ammonia production
- Avoid alcohol entirely, as it directly impairs liver function and worsens ammonia clearance
Supplements
- Lactulose (prescribed): 15–30 mL 2–4 times daily as directed by a physician to trap and eliminate gut ammonia
- Rifaximin 550 mg twice daily (prescription): a non-absorbed antibiotic that reduces ammonia-producing gut bacteria
- Zinc supplementation 25–50 mg daily, as zinc deficiency impairs urea cycle enzymes and is common in liver disease
- Branched-chain amino acids (BCAAs) 10–15 g daily: may improve protein tolerance and reduce ammonia in patients with hepatic encephalopathy
- Probiotics containing Lactobacillus species: may help shift gut microbiome to reduce ammonia-producing bacteria
Related Biomarkers
Frequently Asked Questions
What symptoms indicate high ammonia levels in the blood?
Elevated blood ammonia commonly causes neurological and cognitive symptoms because ammonia is toxic to the brain. Early signs include confusion, forgetfulness, difficulty concentrating, mood changes, and slurred speech. As levels rise, symptoms can progress to tremors (asterixis or 'flapping tremor'), extreme drowsiness, disorientation, personality changes, and eventually loss of consciousness or coma. This constellation of symptoms is called hepatic encephalopathy when associated with liver disease. Any sudden cognitive changes in someone with known liver disease should prompt immediate medical evaluation.
Can you have high ammonia levels with a normal-looking liver function test?
Yes, this is possible. Standard liver function tests like ALT, AST, and bilirubin reflect liver cell damage and bile flow, but they do not directly measure the liver's metabolic capacity. In conditions like portosystemic shunting or certain urea cycle disorders, the liver cells themselves may appear relatively intact, yet ammonia detoxification is severely compromised. Conversely, some patients with well-compensated cirrhosis can have near-normal ALT and AST while still having impaired ammonia processing. Ammonia testing provides unique information that standard liver panels cannot fully capture.
How is an ammonia blood test performed and are there special preparation steps?
An ammonia test requires a blood draw, usually from a vein in your arm. Critically, the sample must be collected into a specific chilled tube, placed on ice immediately, and processed by the laboratory within 15–30 minutes. Physical activity, smoking, and even clenching your fist during the draw can falsely elevate ammonia levels. For this reason, you should avoid strenuous exercise for at least 8 hours before the test, rest quietly before the draw, and not use a tourniquet any longer than necessary. Because of these sensitivity issues, it's important that the test is performed correctly to avoid misleading results.