New Confusion or Altered Mental Status
You or a caregiver notices new confusion, disorientation, drowsiness, or a flipped sleep-wake pattern — possible signs of hepatic encephalopathy — especially if you have known liver disease.
AI Summary An ammonia blood test measures ammonia, a waste product the liver normally clears. Doctors order it when someone with liver disease has confusion or drowsiness. Typical venous levels are about 15–45 mcg/dL, though labs vary. High levels can come from liver disease, shunting, GI bleeding, infection, dehydration, or certain medications. The result alone does not diagnose hepatic encephalopathy. Treatment targets triggers and uses lactulose, with rifaximin added to prevent recurrence.
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Ammonia Levels
Medically Reviewed.
An ammonia blood test measures the amount of ammonia — a waste product from protein breakdown — circulating in your blood. A healthy liver normally converts ammonia into urea for the kidneys to remove; when the liver can't keep up, ammonia can build up and affect brain function.
Doctors most often order this test when someone with liver disease develops confusion, drowsiness, or other signs of hepatic encephalopathy (HE), or to help assess risk in acute liver failure. An ammonia level alone does not confirm or grade HE — it works alongside your symptoms, history, and other tests.
This page explains what an ammonia test involves, why your doctor might order one, how to think about your results, what can raise ammonia levels, and how elevated ammonia is treated and monitored.
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Ammonia Test Basics
What Is an Ammonia Blood Test?
Ammonia is a natural waste product made when your body breaks down protein, both from food and from bacteria in your gut. A healthy liver clears ammonia from the blood by converting it into urea through a process called the urea cycle; your kidneys then remove urea in urine.
When the liver is damaged — as in cirrhosis or acute liver failure — or when blood bypasses the liver through portosystemic shunting, ammonia can build up in the bloodstream. High ammonia is linked to hepatic encephalopathy (HE), a decline in brain function that can cause confusion, drowsiness, or personality changes.
An ammonia blood test is a simple blood draw. It does not require imaging or a procedure like a percutaneous liver biopsy, and your doctor can repeat it as needed. Ask your care team whether you need to fast before the draw, since fasting requirements can vary depending on what other tests are ordered at the same time.
When Doctors Check Ammonia
Why You Might Need an Ammonia Test
Your doctor may check your ammonia level in several situations.
Known Advanced Liver Disease
You have cirrhosis, acute liver failure, or another advanced liver condition, and your doctor wants additional information alongside your symptoms and other liver tests.
Monitoring HE Treatment
You've been diagnosed with hepatic encephalopathy and your care team is tracking how you respond to treatments such as lactulose or rifaximin.
Evaluating Unexplained Symptoms
Your doctor is working through possible causes of confusion or personality changes and wants to help rule liver-related causes in or out.
Ammonia Reference Ranges
Ammonia Levels at a Glance
Ammonia results are usually reported in micrograms per deciliter (mcg/dL) or micromoles per liter (µmol/L), and normal ranges vary by lab and by whether the sample is venous or arterial.
Blood ammonia (venous)
The main measure of how much ammonia is circulating in your blood at the time of the draw.
About 15–45 mcg/dL (11–32 µmol/L), varies by lab
Not usually a concern on its own.
Typical for someone without significant liver dysfunction.
May reflect reduced liver clearance of ammonia, GI bleeding, dehydration, certain medications, or rare metabolic conditions; interpreted together with your symptoms and other liver tests.
Arterial ammonia (acute liver failure)
In hospitalized patients with acute liver failure, doctors sometimes use an arterial sample and higher-risk thresholds.
Risk rises above about 75–100 µmol/L
Associated with lower risk of intracranial hypertension in this setting.
Below roughly 75 µmol/L is considered lower risk.
Levels above 100 µmol/L raise the risk of severe encephalopathy, and levels above 150–200 µmol/L are linked to a higher risk of brain swelling (intracranial hypertension).
Ammonia Is One Piece of the Picture
An elevated ammonia level alone does not confirm or grade hepatic encephalopathy in people with chronic liver disease, and a normal level does not fully rule it out — though it makes HE less likely. Ammonia testing is most useful alongside your symptoms, exam findings, and other tests.
High Ammonia Causes
What Can Raise Ammonia Levels
Liver Disease and Reduced Clearance
Cirrhosis, acute liver failure, and other conditions that damage the liver reduce its ability to convert ammonia into urea, allowing it to build up in the blood.
Portosystemic Shunting
In advanced liver disease, blood can bypass the liver through alternate vessels, including a surgically placed shunt such as a TIPS. Ammonia-rich blood then reaches the brain without being filtered.
GI Bleeding and Constipation
Bleeding in the digestive tract and constipation both increase the amount of protein broken down by gut bacteria, raising ammonia production and absorption.
Infection, Dehydration, and Certain Medications
Infections, dehydration, some diuretics, and sedating medications are common triggers that can push ammonia levels up and precipitate hepatic encephalopathy.
Rare Non-Liver Causes
Inherited urea cycle disorders, kidney failure, and certain medications can raise ammonia even without liver disease; your doctor will consider these if your liver tests are otherwise normal.
Clinical Context and Limits
How Ammonia Relates to Hepatic Encephalopathy
Ammonia Does Not Diagnose or Grade HE on Its Own
Elevated ammonia is common in people with hepatic encephalopathy, but increased blood ammonia alone does not add diagnostic, staging, or prognostic value for HE in people with chronic liver disease. Doctors diagnose and grade HE mainly from your history, symptoms, and exam — not from the ammonia number by itself.
A Normal or High Result Needs Context
A normal ammonia level makes an active episode of overt HE less likely and can prompt your doctor to look for other causes of confusion. But because ammonia levels can be normal even when HE is present, and can be high in people without any HE symptoms, your care team weighs the result alongside cognitive assessments, such as those used in [neurocognitive testing](/liver-tests/liver-complication-testing/hepatic-encephalopathy-evaluation/neurocognitive-testing) or the [HAST/HASA score](/liver-tests/medical-scores/hepatic-encephalopathy-scores/hast-hasa-score).
Ammonia Matters More in Acute Liver Failure
In acute liver failure, persistently elevated ammonia is treated differently: arterial ammonia above roughly 100 µmol/L is linked to a higher risk of severe encephalopathy, and levels above 150–200 µmol/L are a significant predictor of intracranial hypertension (brain swelling). In this setting, ammonia helps guide decisions about ICU monitoring and treatment intensity.
Treatment Focuses on Triggers and Ammonia-Lowering Therapy
Treating the trigger is often the most effective step. Common precipitating factors for an HE episode include infections, gastrointestinal bleeding, constipation, dehydration, and sedating medications. First-line treatment for an HE episode is [lactulose](/liver-therapies/liver-disease-complication-management/hepatic-encephalopathy/lactulose), which reduces ammonia production and absorption in the gut; [rifaximin](/liver-therapies/liver-disease-complication-management/hepatic-encephalopathy/xifaxan) is commonly added to prevent recurrence after a second episode.
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Common Questions
Answers to Common Ammonia Levels Questions
What is a normal ammonia level?
A normal venous ammonia level is typically about 15–45 mcg/dL (11–32 µmol/L), though exact ranges vary by lab. Your report lists the range that lab uses, and ranges also differ depending on whether the sample is venous or arterial. A normal result makes an active episode of hepatic encephalopathy less likely. It does not fully rule HE out, so your doctor also considers your symptoms and exam. If you have clear signs of overt HE but a normal ammonia level, your doctor should re-evaluate the diagnosis.
Does a high ammonia level mean I have liver disease or hepatic encephalopathy?
Not necessarily. Ammonia can rise from causes unrelated to the liver, such as GI bleeding, dehydration, certain medications, kidney problems, or rare inherited urea cycle disorders. In people with known liver disease, a high level supports a diagnosis of hepatic encephalopathy but does not confirm it. An increased blood ammonia level alone adds no diagnostic, staging, or prognostic value for HE in chronic liver disease. Doctors rely mainly on your history, symptoms, and exam, along with other tests. If you or someone you know becomes suddenly and severely confused, seek medical attention right away.
Do I need to fast before an ammonia blood test?
Usually not for the ammonia test itself, but ask your doctor first. Other tests ordered at the same time may require fasting, and requirements vary. Try to avoid vigorous exercise right before the draw, since muscle activity can temporarily raise ammonia. The test is a simple blood draw, and your doctor can repeat it as needed.
How is a high ammonia level treated?
Treatment focuses on lowering ammonia and fixing whatever triggered the rise. The first-line medicine for an HE episode is lactulose, which reduces how much ammonia the gut makes and absorbs. After an episode is controlled, doctors also use it to help prevent another one. Rifaximin is an antibiotic that reduces ammonia-producing bacteria in the gut. Doctors usually add it to lactulose for people who have had a recurrence while on lactulose alone. Lactulose can cause digestive side effects, so tell your care team if confusion worsens or bowel movements become excessive. Treating the trigger is just as important. Common triggers include infection, GI bleeding, constipation, dehydration, and sedating medications. Often, treating the trigger resolves the episode.
Should I cut protein out of my diet if my ammonia is high?
No. Protein restriction is not recommended for hepatic encephalopathy because it can worsen malnutrition and muscle loss. For clinically stable adults with cirrhosis, the usual goal is about 1.2–1.5 g/kg/day of protein. Eggs, cheese, fish, and poultry may be better tolerated than red meat. When supplementation is needed, vegetarian protein sources may be preferred because of their favorable effects on ammonia metabolism. Eating consistent meals also helps. Ask your care team for a protein plan that fits your condition.
Medical disclaimer: LiverDirectory provides educational information and a directory of providers. It does not provide medical advice, diagnosis, or treatment. Always consult a licensed physician regarding any medical condition.