Increased Levels

• Rising ammonia levels indicate a disruption in the urea cycle and the inability of the liver to metabolize ammonia. High levels may lead to lethargy and coma, according to LabTestsonline.com.
  
  

Causes of Increased Levels

• Besides liver diseases like cirrhosis and hepatitis, enzymatic problems in the urea cycle, kidney damage, smoking and drugs like diuretics and barbiturates can raise ammonia levels.
  
  

Decreased Levels

• Low levels of ammonia have less significance. High blood pressure and the use of antibiotics like neomycin can lower ammonia levels.
  
  

Testing

• Testing for ammonia involves drawing a blood sample from a vein. A doctor will typically order other tests at the same time, like liver function tests to screen for liver disease or monitor a treatment for liver disease, according to WebMD.com.
  
  

Normal Levels

• Normal blood serum levels are less than 35 micromoles per liter.