For adults, a normal blood ammonia level falls between 15 and 45 µg/dL (roughly 11 to 32 µmol/L). Levels above 60 µmol/L generally signal a problem, and once blood ammonia climbs past 100 to 200 µmol/L, the risk of serious brain damage rises sharply. For inhaled ammonia gas, concentrations above 300 ppm are immediately dangerous to life.
Those numbers shift depending on your age, whether the exposure is in your blood or in the air, and how long it lasts. Here’s what the thresholds actually mean in practical terms.
Normal Blood Ammonia Levels
Your body produces ammonia constantly as it breaks down protein. The liver converts most of it into a harmless waste product that leaves through urine. A healthy adult typically measures between 15 and 45 µg/dL. Newborns run higher, with a normal reference range up to about 100 µmol/L, dropping to 50 µmol/L or below after the neonatal period. Lab reference ranges vary slightly depending on the testing method, so your results will usually come with the specific lab’s normal range printed alongside them.
When Blood Ammonia Becomes Dangerous
The danger isn’t a single cutoff but a gradient. As ammonia rises, the brain takes the hardest hit because it’s especially vulnerable to the toxic effects. Here’s how symptoms and risks escalate:
- 100 to 150 µmol/L: In newborns, this is where symptoms begin. Babies become lethargic, irritable, and may vomit. Adults at this range can develop impaired concentration, slurred speech, hand tremors, and disorientation.
- 200 µmol/L and above: Seizures, encephalopathy (a broad term for brain dysfunction), and coma become real risks. In patients with acute liver failure, arterial ammonia above 200 µg/dL is strongly associated with dangerous brain swelling. In pediatric intensive care, reaching this threshold within 48 hours of admission carries roughly five times the risk of death at 28 days.
- 300 µmol/L and above: Widely considered a sign of severe crisis requiring aggressive treatment.
- 500 µmol/L and above: Current treatment guidelines call for dialysis at this level, though some experts argue that dialysis should start sooner.
- 1,000 µmol/L and above: Survival is possible but uncommon. Prognosis is generally considered poor, especially if the crisis lasts longer than 24 hours.
These thresholds apply most directly to acute situations. In chronic liver disease, the picture is muddier.
Ammonia Levels in Liver Disease
If you or someone you know has cirrhosis or another chronic liver condition, ammonia levels can be surprisingly misleading. One study found that 69% of patients with no signs of brain dysfunction still had ammonia readings above normal. That means a high number doesn’t automatically mean encephalopathy, and a normal number doesn’t rule it out. Doctors diagnosing hepatic encephalopathy in people with known liver disease rely more on clinical symptoms (confusion, personality changes, sleep disruption, tremors) than on the ammonia number itself.
Where the blood test does carry real weight is in acute liver failure, a sudden and severe loss of liver function in someone who may not have had prior liver problems. In that setting, high ammonia levels help predict who is at risk for life-threatening brain swelling and guide treatment urgency.
Dangerous Levels of Ammonia Gas
Ammonia in the air is a separate concern, measured in parts per million (ppm) rather than blood concentrations. This matters for people who work around industrial refrigeration, fertilizer, or cleaning chemicals. The thresholds stack up like this:
- 25 ppm: The level at which most people start noticing mild irritation. This is the recommended workplace exposure limit for an 8-hour shift set by NIOSH, with a short-term ceiling of 35 ppm. OSHA allows up to 50 ppm over 8 hours.
- 300 ppm: The “immediately dangerous to life or health” threshold. At this concentration, you need to leave the area right away. Exposure between 300 and 500 ppm is tolerable for only about 30 minutes to an hour before causing serious respiratory harm.
- 500 ppm: Causes significant changes in breathing rate and moderate to severe irritation of the eyes, nose, and throat even in short exposures.
- 5,000 to 10,000 ppm: Reported to be fatal.
Ammonia gas has a sharp, unmistakable smell. Most people can detect it at concentrations well below harmful levels, which serves as a natural warning system. The danger increases in enclosed spaces where the gas can accumulate quickly.
Why Ammonia Test Results Can Be Wrong
Blood ammonia is one of the trickiest lab tests to get right. The sample starts generating extra ammonia the moment it’s drawn, because blood cells break down an amino acid into ammonia on their own. To get an accurate reading, the sample needs to be transported on ice, separated from blood cells within 15 minutes of the draw, and analyzed within 20 to 30 minutes.
Delays at any step can push the result artificially higher. Even environmental factors matter: smoking a cigarette before the draw or having ammonia-based cleaning products nearby can contaminate the sample. If your result comes back unexpectedly high and you feel fine, a repeat test with careful sample handling is a reasonable next step. People with high white blood cell or platelet counts are especially prone to false elevations because those cells produce more ammonia in the tube.
Newborns and Children Face Higher Risk
Ammonia is especially toxic to a developing brain. In newborns with undiagnosed metabolic conditions like urea cycle disorders, ammonia can spike within the first few days of life. The initial symptoms, lethargy, poor feeding, vomiting, look like dozens of other newborn problems, which makes early recognition difficult.
Untreated, severe neonatal hyperammonemia can cause irreversible damage including uncontrolled seizures, cerebral palsy, and profound cognitive impairment. Current protocols define a hyperammonemic crisis in children as plasma ammonia at or above 150 µmol/L with related symptoms. Some researchers have argued that dialysis should begin at lower thresholds than the current 500 µmol/L guideline, since earlier intervention may improve outcomes. Peak ammonia levels above 180 µmol/L at symptom onset have been linked to poor enough outcomes that some centers recommend dialysis at that point rather than waiting.