A normal blood ammonia level ranges from 15 to 45 micrograms per deciliter, according to MedlinePlus. Consuming alcohol, eating a diet high in protein or taking medications such as narcotics, valproic acid or acetazolomide can falsely elevate ammonia levels.
A blood ammonia level is obtained by drawing blood from a vein, states MedlinePlus. Patients are usually required to fast for eight to 12 hours prior to the blood test. Doctors usually order an ammonia blood test to diagnose certain medication conditions or to monitor a severe liver disease called hepatic encephalopathy. High ammonia levels in the blood are toxic and sometimes lead to confusion, lethargy or coma.