Ammonia

Background

• Byproduct of protein metabolism; normally converted to urea by the liver
• Elevated in hepatic dysfunction; correlates poorly with degree of hepatic encephalopathy

Normal Values

• Normal: 15-45 mcg/dL (varies by lab)

Interpretation

• Elevated in hepatic encephalopathy, urea cycle defects, portosystemic shunts, valproic acid toxicity, and urinary tract infections with urea-splitting organisms
• Serum ammonia level does not reliably correlate with severity of encephalopathy
• A normal ammonia level makes hepatic encephalopathy less likely but does not completely exclude it
• Sample handling affects accuracy: specimen must be placed on ice and processed rapidly
• Treatment of elevated ammonia: lactulose, rifaximin, treat underlying cause

See Also

• Hepatic encephalopathy
• Ammonia toxicity
• Liver function tests
• Cirrhosis