This lab test is most commonly ordered to diagnose and monitor hepatic encephalopathy which can happen with severe liver disease.

Ammonia Overview

Reviewed: April 21, 2014

Ammonia is a byproduct of protein metbolism. Protein that has been absorbed from the digestive system and the normal turnover of muscle cells creates ammonia in the body throughout the day. Usually, the liver and kidneys will clear excess ammonia and prevent it from appearing in high levels in the blood.

Ammonia levels are measured in micromoles per liter (micromol/L).

The normal value is less than 40 micromol/L


Blood draw


Fasting 8 hours before the test is required.

Water intake is allowed.

Avoid strenuous exercise and smoking just before the test.

What the results mean

Values above the normal level can indicate heart, lung, and metabolism problems. High ammonia levels in the blood can sometimes be a sign of serious liver damage, hepatitis, and drug overdose. Ammonia can cause mental changes and erratic behaviors, and some evidence shows higher levels of ammonia can lead to more dramatic shifts.