A patient with hepatitis develops hepatic encephalopathy. Which lab result best correlates with this mental status change?

• A. Ammonia 100 mcg/dL
• B. Bilirubin 7 mg/dL
• C. ALT 56 U/L
• D. AST 10 U/L

Answer: (A)

Hepatic encephalopathy is driven by the brain-toxic effects of ammonia that accumulate when the liver can’t detoxify normally. In liver disease, ammonia produced by gut bacteria isn’t efficiently converted to urea and excreted, so it rises in the blood and crosses into the brain. There it causes astrocyte swelling and disrupts neurotransmission, leading to the mental status changes seen in encephalopathy. That direct link between elevated ammonia and brain function makes the ammonia level the best lab correlate of the cognitive changes.

Bilirubin reflects the liver’s ability to excrete bile pigments and often indicates cholestasis or overall liver clearance issues, but it doesn’t explain neurotoxic effects. ALT and AST indicate hepatocellular injury, showing damage to liver cells, yet they don’t quantify the toxin load affecting the brain or the risk of encephalopathy.