Ammonia, Plasma Ammonia

This is a test to detect elevated levels of ammonia in the blood, to evaluate changes in consciousness, or to help diagnose hepatic encephalopathy and Reye's syndrome. It may be ordered when a patient experiences mental changes or lapses into a coma of unknown origin; if an infant or child experiences frequent vomiting and increased lethargy as a newborn or about a week after a viral illness.

Ammonia is a compound produced by intestinal bacteria and by cells in the body during the digestion of protein. Ammonia is a waste product that the liver changes into urea and glutamine. The urea is then carried by the blood to the kidneys, where it is put out in the urine. If this "urea cycle" does not complete, ammonia builds up in the blood. This also happens when you cannot put out urine (kidney failure) or when your liver does not work (hepatic failure). A build up of ammonia in the body can cause mental and neurological changes that can lead to confusion, disorientation, sleepiness, and eventually to coma and even death. Infants and children with increased ammonia levels may vomit frequently, be irritable, and be increasingly lethargic. Left untreated, they may experience seizures, respiratory difficulty, and may lapse into a coma and die.


No preparation or fasting is necessary. A blood sample is taken by a needle from a vein.

  • Avoid exercising before this test.


Normal values depend on the method used for testing. Test results depend on many factors including age, sex, etc. Your lab report should include the specific reference range for your test. Your caregiver will go over you test results with you.

  • Adults: 10-80 mcg/dL (6-47 micromol/L)

  • Neonates, 0 to 10 days (enzymatic): 170-341 mcg/dL (100-200 micromol/L)

  • Infants and toddlers, 10 days to 2 years (enzymatic): 68-136 mcg/dL (40-80 micromol/L)

  • Children, older than 2 years (enzymatic): 19-60 mcg/dL (11-35 micromol/L)

Ranges for normal findings may vary among different laboratories and hospitals. You should always check with your doctor after having lab work or other tests done to discuss the meaning of your test results and whether your values are considered within normal limits.


Your caregiver will go over the test results with you and discuss the importance and meaning of your results, as well as treatment options and the need for additional tests if necessary.


It is your responsibility to obtain your test results. Ask the lab or department performing the test when and how you will get your results.