Blood Ammonia Levels and Clinical Significance

Normal Ranges and Hyperammonemia

Normal blood ammonia concentrations are ≤35 μmol/L (≤60 μg/dL) in adults 1
For neonates aged 1-7 days, normal blood ammonia concentrations are ≤110 μmol/L (≤154 μg/dL) 2, 3
For infants aged 8-14 days, normal blood ammonia concentrations are <90 μmol/L (≤126 μg/dL) 2, 3
For individuals aged 15 days to adulthood, normal blood ammonia concentrations are 16-53 μmol/L (22-74 μg/dL) 2, 3
Hyperammonemia is defined as >100 μmol/L (170 μg/dL) in neonates 1, 4
Hyperammonemia is defined as ≥50 μmol/L (85 μg/dL) in term infants, children, and adults 1, 4
Levels >200 μmol/L (341 μg/dL) are associated with poor neurological outcomes 1, 4
Severe hyperammonemia (>400 μmol/L or 681 μg/dL) may require kidney replacement therapy in pediatric patients 2

Accurate ammonia measurement requires proper sample collection and handling, including collecting blood from a free-flowing venous or arterial sample 2
Use lithium heparin or EDTA tubes for sample collection 2, 5
Transport sample on ice immediately to the laboratory 2, 5
Process within 15 minutes of collection and analyze immediately 2
Collect from fasting patients when possible 5
Avoid venous stasis (tourniquet, fist clenching) 5
Clean skin thoroughly before collection 5
Fill tube completely, secure lid, and homogenize by inversion 5

Ammonia levels alone should not be used to confirm hepatic encephalopathy, as levels may be elevated in cirrhotic patients without encephalopathy 5, 6
A normal ammonia value casts doubt on the diagnosis of hepatic encephalopathy 5, 6
Ammonia levels correlate with the severity/grade of hepatic encephalopathy and prognosis 5, 6
Elevated ammonia levels >100 μmol/L with family history of liver disease, neurological disorders, or severe neurological impairment should prompt investigation for inherited metabolic disorders 5
Sample hemolysis can falsely elevate ammonia results 5
Delayed processing leads to falsely elevated levels 5
High lipemia and jaundice can interfere with ammonia measurement 5
High-protein diet, smoking, exercise, and certain drugs can affect ammonia levels 5
If delayed measurement is necessary, centrifuge at +4°C and freeze the supernatant at −70/−80°C 5