Ammonia concentrations are usually measured to evaluate

• A. Acid-base status
• B. Glomerular filtration
• C. Hepatic encephalopathy
• D. Renal failure

Answer: (C)

Ammonia is normally converted to urea by the liver, so when liver function is impaired, ammonia builds up and can cause brain dysfunction. That link makes ammonia measurements most useful for evaluating hepatic encephalopathy in patients with liver disease. It isn’t a standard test for acid-base status, which is assessed by pH, bicarbonate, and CO2, nor is it a primary marker for renal function or glomerular filtration, which are evaluated with creatinine, BUN, and GFR.