The ammonia test measures the amount of ammonia in a blood . High level of ammonia in blood mey be due to cirrihosis of liver or severe hepatitis.The ammonia test is primarily used to help investigate the cause of changes in behavior and consciousness. It may be ordered, along with other tests such as Blood sugar, electrolytes, and kidney and liver function tests, to help diagnose the cause of a coma of unknown origin or to help support the diagnosis of Reye's syndrome or hepatic encephalopathy caused by various liver diseases.