What is a normal ammonia level in a blood test?

Normal Blood Ammonia Levels

Normal blood ammonia concentrations are ≤35 μmol/L (≤60 μg/dL) in adults. 1

Age-Specific Normal Ranges

• For neonates aged 1-7 days: ≤110 μmol/L (≤154 μg/dL) 2
• For infants aged 8-14 days: <90 μmol/L (≤126 μg/dL) 2
• For individuals aged 15 days to adulthood: 16-53 μmol/L (22-74 μg/dL) 2

Clinical Significance of Ammonia Levels

• Hyperammonemia is defined as:

  • 100 μmol/L (170 μg/dL) in neonates 1, 3

  • ≥50 μmol/L (85 μg/dL) in term infants, children, and adults 1, 3
• Levels >200 μmol/L (341 μg/dL) are associated with poor neurological outcomes 1, 3
• Severe hyperammonemia (>400 μmol/L or 681 μg/dL) may require kidney replacement therapy in pediatric patients 2

Proper Sample Collection and Handling

Accurate ammonia measurement requires proper sample collection and handling:

• Collect blood from a free-flowing venous or arterial sample 2, 4
• Use lithium heparin or EDTA tubes 2
• Transport sample on ice immediately to the laboratory 2
• Process within 15 minutes of collection and analyze immediately 2, 4
• Collect from fasting patients when possible 2
• Avoid venous stasis (tourniquet, fist clenching) 2
• Clean skin thoroughly before collection 2
• Fill tube completely, secure lid, and homogenize by inversion 2

Common Pitfalls in Ammonia Measurement

• Sample hemolysis can falsely elevate results 2
• Delayed processing leads to falsely elevated levels 2, 4
• High lipemia and jaundice can interfere with measurement 2
• High-protein diet, smoking, exercise, and certain drugs can affect levels 2
• If delayed measurement is necessary, centrifuge at +4°C and freeze the supernatant at −70/−80°C 2

Clinical Context

• Ammonia levels alone should not be used to confirm hepatic encephalopathy, as levels may be elevated in cirrhotic patients without encephalopathy 2
• However, a normal ammonia value casts doubt on the diagnosis of hepatic encephalopathy 2
• Ammonia levels correlate with the severity/grade of hepatic encephalopathy and prognosis 2
• 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 2