In acute liver failure, which lab finding best explains the decreased level of consciousness?

• A. Subnormal serum glucose and elevated serum ammonia levels.
• B. Elevated liver enzymes and low serum protein level.
• C. Subnormal clotting factors and platelet count.
• D. Elevated BUN and creatinine levels and hyperglycemia.

Answer: (A)

In acute liver failure, the brain’s function declines mainly because ammonia can no longer be detoxified by the failing liver. Ammonia is produced from intestinal nitrogen and, without conversion to urea, it accumulates in the blood and crosses into the brain, altering neurotransmission and causing cerebral edema and encephalopathy that lead to a decreased level of consciousness. At the same time, the liver’s impaired ability to perform gluconeogenesis and maintain blood glucose can cause hypoglycemia, depriving brain cells of fuel and further worsening mental status.

That combination—high ammonia causing neurotoxic effects and low glucose reducing cerebral energy supply—best explains the change in consciousness in acute liver failure.

Other options point to liver injury markers or complications (like elevated enzymes and low albumin, or coagulopathy, or kidney-related changes) but none directly account for the acute change in mental status the way ammonia buildup paired with hypoglycemia does.