Which of the following disorders is not associated with an elevated blood ammonia level?

• A. Reye syndrome
• B. Renal failure
• C. Chronic liver failure
• D. Diabetes mellitus

Answer: (D)

Ammonia is normally cleared from the blood mainly by the liver turning it into urea. When the liver is damaged or kidney function is compromised, ammonia builds up in the blood, leading to hyperammonemia. Reye syndrome causes acute hepatic dysfunction with high ammonia, and renal failure reduces excretion of ammonia, also raising levels. Chronic liver failure similarly impairs ammonia detoxification, causing elevation. Diabetes mellitus, on the other hand, does not inherently cause elevated ammonia levels, as its primary metabolic disturbances are in glucose and fat metabolism rather than ammonia detoxification. So the disorder not associated with elevated blood ammonia is diabetes mellitus.