Lab result explainedLiverLast updated November 10, 2026

Ammonia blood test: what high ammonia levels mean for your liver and brain

Ammonia (blood) (NH3) · Ammonia (stand-alone test, drawn on ice) · reported in µg/dL (SI µmol/L; µg/dL × 0.587 = µmol/L)

Ammonia is a nitrogen waste product made mainly when bacteria in the gut break down protein and when the body's own cells break down amino acids. In health, nearly all of it is captured by the liver and converted to urea through the urea cycle, then excreted by the kidneys, so very little reaches the general circulation. A blood ammonia test measures what gets through. In adults the usual range is about 15 to 45 µg/dL (11 to 32 µmol/L), and laboratories differ by more than most tests because the measurement is so sensitive to how the sample is handled.

Ammonia is toxic to the brain, and a high level is the main reason people with advanced liver disease become confused, drowsy and eventually comatose, a condition called hepatic encephalopathy. The test is ordered when someone with cirrhosis or acute liver failure develops confusion, when a child or adult has unexplained vomiting, lethargy or confusion that could be an inherited urea cycle disorder, and when a medication such as valproate is suspected of raising it. In cirrhosis a normal ammonia argues strongly against hepatic encephalopathy, but a high value correlates only loosely with how confused someone is, so the number is used to support the diagnosis rather than to grade it.

The most common cause of a surprising high ammonia is the blood draw itself. Ammonia rises within minutes in a tube left at room temperature, with a tourniquet left on, with a clenched fist, with hemolysis, and after smoking, so the sample must be taken without stasis, placed on ice immediately and analyzed within about 15 to 30 minutes. A mildly high result in someone who feels well and has no liver disease is repeated under those conditions before anything is concluded. A high ammonia in someone with confusion, vomiting or drowsiness, however, is an emergency whatever the cause.

NH3 at a glance

What it is: the nitrogen waste product the liver normally converts to urea; it rises when the liver cannot clear it, when blood bypasses the liver, or when too much is produced.
Normal (adults): about 15–45 µg/dL (11–32 µmol/L); some labs allow up to 60 µg/dL. Newborns run higher, up to about 90–100 µmol/L in the first days.
High ammonia: cirrhosis with hepatic encephalopathy, acute liver failure, portosystemic shunts, gastrointestinal bleeding, urea cycle disorders, valproate and some other drugs, urinary infection with urease-producing bacteria, and poor sample handling.
Danger thresholds: in acute liver failure an arterial ammonia above 100 µmol/L (about 170 µg/dL) predicts severe encephalopathy and above 200 µmol/L predicts brain swelling; in a newborn, above 150 µmol/L with no other explanation means a urea cycle disorder until proven otherwise.
Low ammonia is not a medical problem; it has no lower limit of concern.
Next step: confirm the sample was drawn correctly, look for a trigger (infection, bleeding, constipation, dehydration, sedatives, new drugs), check liver tests, INR, glucose and electrolytes, and treat the cause; any confusion or drowsiness with a high ammonia needs same-day care.

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What NH3 measures

Most of the body's ammonia is made in the intestine, where bacteria deaminate dietary protein and urea, and in the gut wall itself, which breaks down glutamine for energy. It travels in the portal vein straight to the liver, where the urea cycle, a chain of five enzymes, converts it to urea; the liver clears about 90 percent of the ammonia reaching it in a single pass. Muscle and brain can also mop up ammonia temporarily by attaching it to glutamate to form glutamine. The kidneys both make ammonia (more when potassium is low) and excrete it.

Ammonia reaches the general circulation when the liver's capacity is reduced (cirrhosis, acute liver failure), when portal blood bypasses the liver through shunts (which cirrhosis creates and procedures such as TIPS deliberately open), when a urea cycle enzyme is missing or partly deficient, or when production outstrips clearance, as with a large bleed into the gut, a urinary infection with bacteria that split urea, severe muscle exertion or seizures. In the brain, excess ammonia is converted to glutamine inside astrocytes, which swell; this osmotic swelling underlies the confusion of hepatic encephalopathy and the life-threatening brain edema of acute liver failure.

The lab measures ammonia enzymatically in plasma, usually from a venous sample collected in an EDTA or heparin tube that is placed on ice immediately and centrifuged and analyzed within 15 to 30 minutes, because red cells and plasma enzymes keep generating ammonia in the tube; concentrations can rise by 20 percent or more within an hour at room temperature. Arterial samples read slightly higher than venous and are preferred in acute liver failure research, but venous samples drawn correctly are adequate in practice. Results are reported in µg/dL in the US and µmol/L elsewhere (µg/dL multiplied by 0.587 gives µmol/L).

Normal range for NH3

Reference ranges vary between labs and by age, sex and pregnancy. Use the range printed on your own report.

Group	Typical range (µg/dL (SI µmol/L; µg/dL × 0.587 = µmol/L))	Notes
Adults	15–45 µg/dL (11–32 µmol/L)	Labs vary widely, some up to 60 µg/dL or 35–50 µmol/L. Use the printed range and note whether the sample was handled on ice.
Children (over 1 month)	Up to about 85 µg/dL (50 µmol/L)	Slightly higher than adults; still requires correct collection.
Newborns, first week	Up to about 90–100 µmol/L (150–170 µg/dL)	Preterm infants can run up to 150 µmol/L. Above 150 µmol/L with a normal anion gap and glucose suggests a urea cycle disorder.
Mildly high	Up to about twice the upper limit	Often sample handling, smoking, recent strenuous exercise, a protein-heavy meal or compensated cirrhosis; repeat with correct collection if unexplained.
Moderately high	About 100–200 µg/dL (60–120 µmol/L)	Typical of hepatic encephalopathy in cirrhosis, gastrointestinal bleeding in liver disease, portosystemic shunts and valproate-related hyperammonemia.
Markedly high	Above 200 µg/dL (above about 120 µmol/L)	Acute liver failure, decompensated urea cycle disorders, severe sepsis with liver involvement. Needs emergency assessment.
Acute liver failure thresholds (arterial)	Above 100 µmol/L; above 200 µmol/L	Above 100 µmol/L predicts progression to severe encephalopathy; above 200 µmol/L is associated with brain swelling and herniation.
Urea cycle disorder crisis	Often above 300–1,000 µmol/L	In newborns, or in older children and adults after a protein load, illness, surgery or childbirth; treated as an emergency with ammonia-scavenging drugs or dialysis.

High ammonia (hyperammonemia)

In someone with known liver disease, a high ammonia supports the diagnosis of hepatic encephalopathy, the spectrum of brain dysfunction that runs from subtle slowing and sleep reversal through confusion and a flapping tremor to coma. The relationship between the number and the symptoms is loose: people with cirrhosis commonly walk around with an ammonia of 60 to 100 µg/dL and clear thinking, and someone with a level of 150 µg/dL may be only mildly confused while another is stuporous. The American and European liver associations therefore advise that ammonia should not be used to grade encephalopathy or to decide treatment on its own, but that a normal level in a confused person with cirrhosis makes encephalopathy unlikely and should prompt a search for other causes such as bleeding in the brain, infection, drugs or low sodium. Encephalopathy in cirrhosis almost always has a trigger: infection, gastrointestinal bleeding, constipation, dehydration from diuretics, low potassium, sedatives or opioids, or too much alcohol.

In acute liver failure the number matters more. Arterial ammonia above 100 µmol/L (about 170 µg/dL) predicts the development of severe encephalopathy, and sustained levels above 150 to 200 µmol/L are associated with brain swelling and herniation, which is the main cause of death in the first days. Serial ammonia measurements are part of intensive care monitoring and help decide on transplant listing.

A high ammonia in someone without liver disease is a different problem and must not be dismissed. In a newborn with vomiting, poor feeding, lethargy or rapid breathing, an ammonia above 150 µmol/L with a normal anion gap and normal glucose is an inherited urea cycle disorder until proven otherwise, and every hour of delay worsens the brain injury. Partial deficiencies, especially of ornithine transcarbamylase (OTC), can surface for the first time in adolescence or adulthood as episodes of confusion, vomiting or psychiatric symptoms triggered by a high-protein meal, fasting, infection, surgery, childbirth or starting valproate; a lifelong dislike of meat is a clue. Other non-liver causes include valproate and some chemotherapy drugs, urinary infections with urease-producing bacteria in someone with urinary retention, gastrointestinal bleeding, kidney failure, severe exercise or prolonged seizures, and simply a badly handled sample.

Common causes

Cirrhosis with hepatic encephalopathy
A scarred liver clears less ammonia and portal blood is shunted around it. Encephalopathy affects 30 to 45 percent of people with cirrhosis at some point and is nearly always set off by a trigger: infection, gastrointestinal bleeding, constipation, dehydration, low potassium, sedatives, alcohol or a missed lactulose dose.
Acute liver failure
Acetaminophen overdose, viral hepatitis, drug reactions and other causes of sudden liver cell death remove the urea cycle almost entirely; ammonia can exceed 200 µmol/L within days and drives brain swelling.
Portosystemic shunts
Blood vessels that bypass the liver, whether created by cirrhosis, placed deliberately (TIPS) to relieve portal hypertension, or present from birth, deliver gut ammonia straight to the brain. Encephalopathy occurs in 20 to 50 percent of people after TIPS.
Gastrointestinal bleeding
Blood in the gut is a large protein meal; bacteria convert it to ammonia within hours. In someone with liver disease, a bleeding varix or ulcer is one of the commonest triggers of encephalopathy.
Urea cycle disorders
Inherited deficiency of one of the urea cycle enzymes, most often ornithine transcarbamylase (X-linked, so female carriers can be affected). Newborns present with vomiting, lethargy and coma in the first days; partial deficiencies present later with episodic confusion after protein, illness or childbirth. Low BUN, respiratory alkalosis and a normal anion gap are clues.
Valproate and other medications
Valproate raises ammonia in a substantial share of users, often with no symptoms, by inhibiting a urea cycle enzyme and depleting carnitine; confusion or drowsiness on valproate should prompt an ammonia test. Carbamazepine, topiramate, 5-fluorouracil, asparaginase, high-dose chemotherapy and salicylates in children (Reye syndrome) can also raise it.
Urinary tract infection with urease-producing bacteria
Proteus, Klebsiella and some other bacteria split urea in retained urine into ammonia, which is absorbed from a distended bladder; this classically causes confusion with a high ammonia in someone with an enlarged prostate, a neurogenic bladder or a urinary diversion, and a normal liver.
Kidney failure, severe exertion and seizures
The kidneys excrete ammonia, so advanced kidney disease raises it modestly; heavy or prolonged exercise and status epilepticus release ammonia from muscle and can double or triple the level for hours.
Sample handling and smoking
A tourniquet left on, fist clenching, hemolysis, a delay before analysis or a tube not kept on ice can raise ammonia by 20 to 50 percent, and smoking in the hour before the draw adds around 10 µg/dL. This is the commonest reason for an unexpected mild elevation in someone who is well.
Other causes
Severe sepsis, multiple myeloma and other blood cancers, bariatric surgery with protein malnutrition, total parenteral nutrition and infection with ammonia-producing organisms after transplant have all caused hyperammonemia without cirrhosis.

Symptoms that can go with it

None at mildly raised levels, which is common in stable cirrhosis
Forgetfulness, poor concentration, personality change, irritability or sleeping by day and waking at night
A flapping tremor of the outstretched hands (asterixis), slurred speech, slowed movements and an unsteady walk
Confusion and disorientation progressing to drowsiness, stupor and coma
Nausea, vomiting, loss of appetite and headache
In infants: poor feeding, vomiting, floppiness, rapid breathing, irritability and seizures within days of birth
In older children and adults with a urea cycle disorder: episodes of confusion or vomiting after high-protein meals, fasting or illness, and a long-standing aversion to meat
A sweet, musty breath odor (fetor hepaticus) in advanced liver disease

Read it alongside

ALT, AST, bilirubin, albumin and PT/INR — define whether the liver is injured and how well it is functioning; a rising INR with a high ammonia means liver failure.
Glucose — low in acute liver failure and in some urea cycle and organic acid disorders; must be checked in any drowsy child.
Sodium, potassium and bicarbonate — low sodium and low potassium are both triggers of encephalopathy; low potassium increases kidney ammonia production.
Anion gap and blood pH — a urea cycle disorder gives a high ammonia with a normal anion gap and respiratory alkalosis; organic acidemias give a high anion gap acidosis.
BUN — a low BUN with a high ammonia suggests the urea cycle is not working, as in OTC deficiency or acute liver failure.
Lactic acid — rises in sepsis, seizures and liver failure, all of which also raise ammonia.
Plasma amino acids, urine orotic acid and acylcarnitine profile — the specific tests for urea cycle and related metabolic disorders when ammonia is high without liver disease.
CBC, blood and urine cultures, chest X-ray and ascitic fluid analysis — look for the infection that so often precipitates encephalopathy in cirrhosis.

What usually happens next

Ask how the sample was drawn: no tourniquet, on ice, analyzed within 30 minutes. If any of those were not met and you feel well, the test is simply repeated correctly.
In cirrhosis with new confusion, the work-up is for the trigger: cultures and a check for spontaneous bacterial peritonitis, a look for gastrointestinal bleeding, electrolytes and kidney function, a medication review for sedatives and opioids, and a check on bowel frequency; treatment with lactulose and rifaximin is directed by the clinician.
In acute liver failure, ammonia is repeated serially and read with INR, glucose, lactate and mental status to guide intensive care and transplant assessment.
A high ammonia with no liver disease prompts a medication review (valproate especially), a urine culture and bladder scan, plasma amino acids, urine orotic acid and an acylcarnitine profile, and referral to a metabolic specialist if those are abnormal.
Useful questions to ask: what triggered this episode, whether the dose and timing of lactulose or other treatment need adjusting, and whether protein intake has been restricted (it usually should not be).

Diet, lifestyle and natural levers with evidence

What can move NH3 once the cause is known. Nothing here replaces finding the cause.

Do not restrict protein; spread it through the day with a late-evening snack

Strong evidence

Protein restriction, once standard advice, makes encephalopathy worse by driving muscle breakdown, and muscle is the main tissue that removes ammonia when the liver cannot. In a randomised trial of 30 people hospitalized with hepatic encephalopathy, a normal-protein diet (1.2 g/kg a day) resolved encephalopathy as fast as a low-protein diet while causing less muscle breakdown. The AASLD/EASL guideline and the ISHEN consensus recommend 1.2 to 1.5 g of protein per kilogram a day, 35 to 40 kcal/kg, small frequent meals and a late-evening snack of about 50 g of carbohydrate to shorten the overnight fast, which otherwise breaks down muscle. Vegetable and dairy protein are tolerated better than large amounts of red meat.

People with a diagnosed urea cycle disorder follow an individually prescribed protein limit from a metabolic dietitian; this advice is for liver disease, not for them. Glutamine supplements raise ammonia and should be avoided in liver disease.

Branched-chain amino acids (BCAAs)

Moderate evidence

A Cochrane review of 16 randomised trials with 827 participants found that oral BCAA supplements improved hepatic encephalopathy compared with placebo or no intervention (risk ratio 0.73, 95 percent confidence interval 0.61 to 0.88), without changing mortality or quality of life. BCAAs supply muscle with the amino acids it uses to detoxify ammonia into glutamine and help maintain muscle mass; trials typically used 10 to 30 g a day in divided doses for 3 to 24 months.

They do not replace lactulose or rifaximin. Doses large enough to matter add calories and can cause nausea; powders are better tolerated than tablets.

Probiotics and synbiotics

Moderate evidence

A Cochrane review of 21 trials with 1,420 participants found that probiotics, compared with placebo or no treatment, probably improve recovery from hepatic encephalopathy, reduce progression from minimal to overt encephalopathy (risk ratio about 0.3) and lower plasma ammonia by an average of about 8 µmol/L, although the quality of evidence was low and the trials used many different strains, mostly Lactobacillus, Bifidobacterium and Streptococcus mixtures or VSL#3, for 1 to 6 months. The mechanism is a shift away from urease-producing gut bacteria.

Not a substitute for prescribed treatment. Rare bloodstream infections from probiotic organisms have been reported in people with advanced liver disease or central lines; discuss first.

Zinc

Preliminary evidence

Zinc is a cofactor for two urea cycle enzymes and for glutamine synthetase in muscle, and deficiency is common in cirrhosis. A meta-analysis of four randomised trials in 233 people with cirrhosis found that zinc supplementation (typically the equivalent of 50 to 150 mg of elemental zinc a day as zinc sulfate or acetate for 3 to 6 months) improved performance on the number connection test used to detect minimal encephalopathy, with a reduction in ammonia in some trials but no clear effect on overt encephalopathy recurrence.

More than 40 mg of elemental zinc a day for months causes copper deficiency and anemia; higher-dose use needs monitoring. Zinc interferes with some antibiotics and with thyroid medication when taken together.

L-ornithine L-aspartate (LOLA)

Preliminary evidence

LOLA supplies substrates for the urea cycle and glutamine synthesis and is used as a prescription drug in parts of Europe and Asia and sold as a supplement elsewhere. A Cochrane review of 36 randomised trials with 2,377 participants found that LOLA may improve hepatic encephalopathy (risk ratio 0.70) and lower ammonia compared with placebo, but rated the evidence very low quality because of small, poorly reported trials, and found no clear benefit over lactulose or rifaximin.

Oral LOLA products are not FDA-approved and their content is not standardised; the trials with the best results used intravenous preparations in hospital.

Alcohol abstinence, regular bowels and avoiding dehydration

Strong evidence

The everyday triggers of encephalopathy in cirrhosis are things within reach: alcohol, which both injures the liver and depresses the brain; constipation, which lets gut bacteria produce more ammonia (the target on lactulose is two to three soft stools a day); and dehydration from diuretics, vomiting, diarrhea or hot weather, which reduces blood flow to the liver and kidneys. Observational cohorts show that people who stop drinking after a diagnosis of alcohol-related cirrhosis have markedly better survival and fewer episodes of encephalopathy than those who continue.

When to see a clinician promptly

New confusion, unusual drowsiness, difficulty waking, a flapping hand tremor or slurred speech in anyone with liver disease: possible hepatic encephalopathy, needing same-day emergency assessment.
An ammonia above about 100 µmol/L (170 µg/dL) with any change in alertness or behavior, in a child or adult, with or without known liver disease.
A newborn or young child with repeated vomiting, poor feeding, floppiness, rapid breathing or unusual sleepiness: possible urea cycle disorder, an emergency where hours matter.
New confusion, vomiting or drowsiness after starting or increasing valproate, or after a high-protein meal, an illness, surgery or childbirth in someone with a family history of metabolic disorders.
Vomiting blood or passing black, tarry stools in someone with cirrhosis, which triggers encephalopathy and needs emergency care.
Fever, abdominal pain or a swollen abdomen with cirrhosis, which suggest infection of the ascitic fluid, a common trigger that needs same-day antibiotics.

Frequently asked questions

What is a normal ammonia level?

For adults, about 15 to 45 µg/dL, or 11 to 32 µmol/L, though some labs set the upper limit at 60 µg/dL and newborns run considerably higher in the first week. Because the sample must be drawn without a tourniquet, kept on ice and analyzed within about 30 minutes, a mildly high value in someone who feels well is often a collection problem and is repeated before it is taken at face value.

What level of ammonia is dangerous?

There is no single number, because symptoms depend on how fast it rose and on the brain's adaptation. As a guide, in acute liver failure an arterial ammonia above 100 µmol/L (about 170 µg/dL) predicts severe encephalopathy and above 200 µmol/L is associated with brain swelling; in a newborn, above 150 µmol/L suggests a urea cycle disorder; and in a urea cycle crisis levels above 300 to 1,000 µmol/L occur. Any raised ammonia with confusion or drowsiness is an emergency regardless of the exact value.

What causes high ammonia levels without liver disease?

Valproate and some chemotherapy drugs, inherited urea cycle disorders (which can first appear in adults), urinary infections with urease-producing bacteria in someone with urinary retention, gastrointestinal bleeding, kidney failure, prolonged seizures, very heavy exercise, and poor handling of the blood sample. In a child, or in an adult with episodes of confusion after protein-rich meals or illness, a metabolic cause is looked for with plasma amino acids and urine orotic acid.

What are the symptoms of high ammonia?

Early signs are subtle: forgetfulness, poor concentration, personality change, irritability and sleeping by day while awake at night. As the level rises there is confusion, slurred speech, a flapping tremor of the hands, unsteadiness and drowsiness, progressing to stupor and coma. Nausea, vomiting and headache are common. Infants show poor feeding, vomiting, floppiness, rapid breathing and seizures.

Does a high ammonia level mean I have cirrhosis?

Not by itself. Ammonia is high in most people with hepatic encephalopathy, but it also rises with acute liver failure, shunts, bleeding, medications, infections, kidney disease, metabolic disorders and faulty collection, and a well person with stable cirrhosis can have a normal level. Cirrhosis is diagnosed from the history, liver tests, platelet count, imaging and elastography or biopsy, not from ammonia.

How do you lower ammonia levels naturally?

The evidence-based measures are to keep protein intake up (1.2 to 1.5 g/kg a day, spread out, with a late-evening snack) rather than restrict it, to keep bowels moving, to avoid alcohol and dehydration, and, with your clinician's agreement, branched-chain amino acids, probiotics and zinc if you are deficient, each of which has modest trial support. Avoid glutamine supplements. None of these replaces lactulose or rifaximin when they have been prescribed.

Why was my ammonia sample put on ice, and can a bad draw cause a false high?

Yes. Red cells and plasma enzymes keep producing ammonia after the blood leaves the vein, so the level can rise by 20 percent or more within an hour at room temperature. A tourniquet left on, a clenched fist, hemolysis and smoking before the draw also raise it. Ice slows the reaction, which is why the tube goes on ice immediately and is run within 15 to 30 minutes. A result that does not fit the clinical picture is repeated with careful collection before any decision is made.

What does a low ammonia level mean?

Nothing of concern. There is no lower limit at which ammonia causes problems; a low or undetectable result simply means the liver and kidneys are clearing it well. In someone with cirrhosis who is confused, a normal or low ammonia is actually useful, because it points away from hepatic encephalopathy and towards another cause such as infection, bleeding in the brain, low sodium or a medication effect.

References

Ammonia levels. MedlinePlus, US National Library of Medicine (2023)View source
Vilstrup H, Amodio P, Bajaj J, et al.. Hepatic encephalopathy in chronic liver disease: 2014 practice guideline by the American Association for the Study of Liver Diseases and the European Association for the Study of the Liver. Hepatology (2014)
Ong JP, Aggarwal A, Krieger D, et al.. Correlation between ammonia levels and the severity of hepatic encephalopathy. American Journal of Medicine (2003)
Clemmesen JO, Larsen FS, Kondrup J, Hansen BA, Ott P. Cerebral herniation in patients with acute liver failure is correlated with arterial ammonia concentration. Hepatology (1999)
Bernal W, Hall C, Karvellas CJ, Auzinger G, Sizer E, Wendon J. Blood ammonia levels and risk of complications in acute liver failure. Hepatology (2007)
Häberle J, Burlina A, Chakrapani A, et al.. Suggested guidelines for the diagnosis and management of urea cycle disorders: first revision. Journal of Inherited Metabolic Disease (2019)
Amodio P, Bemeur C, Butterworth R, et al.. The nutritional management of hepatic encephalopathy in patients with cirrhosis: International Society for Hepatic Encephalopathy and Nitrogen Metabolism consensus. Hepatology (2013)
Córdoba J, López-Hellín J, Planas M, et al.. Normal protein diet for episodic hepatic encephalopathy: results of a randomized study. Journal of Hepatology (2004)
Gluud LL, Dam G, Les I, et al.. Branched-chain amino acids for people with hepatic encephalopathy. Cochrane Database of Systematic Reviews (2017)
Dalal R, McGee RG, Riordan SM, Webster AC. Probiotics for people with hepatic encephalopathy. Cochrane Database of Systematic Reviews (2017)
Goh ET, Stokes CS, Sidhu SS, Vilstrup H, Gluud LL, Morgan MY. L-ornithine L-aspartate for prevention and treatment of hepatic encephalopathy in people with cirrhosis. Cochrane Database of Systematic Reviews (2018)
Chavez-Tapia NC, Cesar-Arce A, Barrientos-Gutiérrez T, Villegas-López FA, Méndez-Sanchez N, Uribe M. A systematic review and meta-analysis of the use of oral zinc in the treatment of hepatic encephalopathy. Nutrition Journal (2013)
Hepatic encephalopathy. Merck Manual Professional Version (2024)

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This page is educational and is not medical advice or a diagnosis. Lab results have to be interpreted together with your history, symptoms and other results by a clinician who knows you. Do not start or stop a supplement to change a lab value before the cause is known.