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Blood Test Tracker

Ammonia

A waste product made when the body breaks down protein, normally cleared by the liver. The test shows whether ammonia is building up in the blood.

AI-verified against cited sources. Awaiting expert reviewAlso called NH3LOINC 16362-6

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What it is

Ammonia is made by cells all over the body, especially in the intestines, liver and kidneys. The liver turns most of it into urea, which leaves the body in urine. Ammonia is toxic to the brain, so it matters when it builds up. The test is mainly used in people with severe liver disease, and in babies and children when a rare inherited condition of the urea cycle is a question.

Why it matters

When the liver can't clear ammonia well, the level can rise and affect the brain. This can cause confusion, low energy and, in severe cases, coma. The test is most often used to look into and follow hepatic encephalopathy, a brain problem linked to severe liver disease. A single result is only one piece of the picture: ammonia isn't used to screen for liver disease, and doctors read it together with symptoms and other tests.

If it’s high

A level above your lab's range can mean the body is not clearing ammonia well. It can also come from a sample that sat too long before testing, so a surprising result is sometimes repeated.

Common causes

  • A sample that was not kept cold, was delayed, or was drawn with a long tourniquet time
  • Smoking before the test, hard exercise or a high-protein meal
  • Bleeding in the digestive tract
  • Liver failure or severe liver disease, including cirrhosis
  • Kidney disease
  • Some medicines, such as valproic acid, diuretics or barbiturates
  • High body temperature, or poisoning with salicylates such as aspirin (rare)
  • Genetic conditions of the urea cycle (rare)
  • Reye syndrome (rare)

What can help

  • Ask whether the test should be repeated, with the sample handled on ice and tested promptly
  • Ask your clinician how your medicines, diet, kidneys and liver might play a part
  • If you have liver disease, follow your care team's plan for it

What can affect your result

  • Sample handling: delay, warmth or a long tourniquet time can give a falsely high result
  • Smoking, strenuous exercise and a recent high-protein meal
  • Medicines such as valproic acid, diuretics and barbiturates
  • Age: babies and children have their own ranges
  • Lab and method: reported ranges differ several-fold between labs and sources, so the range on your own report is the one to use
  • Handling matters most. Blood cells keep releasing ammonia after the draw, so the sample must be kept cold and spun down quickly. Labcorp asks for the tube to go on ice right away, the plasma to be separated within 15 minutes and the patient not to clench a fist. ARUP's referral listing says to freeze the plasma immediately and rejects refrigerated or room-temperature samples; a published study kept samples on ice and ran them within 60 minutes (Bajaj 2020).
  • Labcorp lists 12 to 14 hours without food before the draw, to avoid a cloudy (lipemic) sample that interferes with the test.
  • A long tourniquet time or fist clenching can raise the result. The Bajaj study used a free-flowing venous sample without a tourniquet.
  • Smoking before the draw and strenuous muscle effort can raise the result (MedlinePlus).
  • A high-protein meal can raise ammonia, especially in people with cirrhosis (Bajaj 2020).
  • Some medicines can raise it, including alcohol, acetazolamide, barbiturates, diuretics, narcotics and valproic acid (MedlinePlus). Don't stop a medicine unless your clinician tells you to.

Reflects the moment of the draw and can change within hours with diet, bleeding in the gut, illness or liver function.

When to talk to a clinician

Seek care the same day for new confusion, unusual sleepiness, slurred speech or a big change in behavior, especially if you have liver disease. Call 911 or your local emergency number if someone is very hard to wake or doesn't make sense. A baby or child with poor feeding, repeated vomiting or unusual sleepiness needs to be seen promptly. Quest Diagnostics treats an ammonia above 200 µmol/L (about 340 µg/dL) as an urgent value for ages 18 and under.

Questions you could ask

  • Why was an ammonia test ordered for me, and what would different results change?
  • Does my lab use a different range for children and adults?
  • Was my sample handled the right way, or should we repeat the test?
  • Could a medicine, a high-protein meal or hard exercise explain this?
  • Do my liver and kidney tests give any clues?

Questions people ask

Why does the blood sample have to go on ice?

Blood cells keep making ammonia after the sample is drawn. If the tube sits at room temperature, the number can climb and look higher than your true level. Labs cool the sample, separate the plasma quickly and test it promptly or freeze it.

Do I need to fast, or avoid smoking or exercise, before the test?

Some labs ask for fasting. Labcorp, for example, lists 12 to 14 hours without food to avoid a cloudy sample, and a large protein meal can raise ammonia, especially in people with cirrhosis. MedlinePlus advises not smoking before the draw, and strenuous muscle effort can raise the level. Follow the instructions your lab or clinician gives you, and don't stop any medicine unless they tell you to.

Does a result in the usual range rule out a liver problem?

No. Ammonia is not used to screen for liver disease, and many liver conditions leave it in the usual range. Tests such as ALT, AST, bilirubin, albumin and INR show more about liver health. Your clinician reads ammonia together with your symptoms.

Show the science and sources

Units

  • 1 µmol/L = 1 µmol/L
  • 1 µmol/L = 1.703 µg/dL

Open the Ammonia unit converter

For clinicians and researchers

Ammonia comes from gut bacteria and enterocyte glutamine metabolism, kidney glutamine handling and amino acid breakdown. The liver clears it through the urea cycle and glutamine synthesis, so liver failure, portosystemic shunting and urea cycle defects raise it. It is a poor screening test: in people with cirrhosis the diagnostic value for hepatic encephalopathy is debated, hepatic encephalopathy can occur with a normal level, and a level in the usual range in someone with altered mental status calls the diagnosis into question (Balcar 2023). In stable outpatients with advanced chronic liver disease, a level of 1.4 times the lab's upper limit or more predicted hepatic decompensation and liver-related admission in that study (Balcar 2023). Pre-analytical handling dominates the result: red cells and plasma enzymes generate ammonia in vitro, so samples go on ice, are separated promptly and are analyzed quickly or frozen. In one multi-site study, fresh and flash-frozen samples correlated only modestly (r=0.62), site-specific upper limits from healthy volunteers differed from routine values, and ammonia rose 12% and 18% one and two hours after a protein meal in cirrhosis (Bajaj 2020). Reference intervals therefore differ several-fold between labs and sources, which is why this entry carries no generic reference range; always use the interval printed on the report. Venous plasma is standard, and results are quoted as ammonia (NH3), not ammonia nitrogen. 1 µg/dL of NH3 is 0.587 µmol/L; the often-quoted 0.714 factor applies to ammonia nitrogen.

LOINC 16362-6 (primary), 22763-7, 35254-2. Specimen: plasma.

Sources

  1. Ammonia, Plasma (test 007054), Labcorp
  2. Ammonia Level, Plasma (test 3019004), ARUP Laboratories
  3. Ammonia blood test, MedlinePlus, National Library of Medicine (2025)
  4. Quest Diagnostics Priority Result Reporting Policy (Client Synopsis), Quest Diagnostics (2025)
  5. Variability and Lability of Ammonia Levels in Healthy Volunteers and Patients With Cirrhosis: Implications for Trial Design and Clinical Practice, The American Journal of Gastroenterology (2020)
  6. Impact of ammonia levels on outcome in clinically stable outpatients with advanced chronic liver disease, JHEP Reports (2023)
  7. Ammonia (PubChem CID 222), PubChem, National Library of Medicine

AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.

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