Overview
- Primarily absorbed from gastrointestinal tract, especially colon. Smaller levels from muscle metabolism.
- Increased levels reflect impaired liver function
or portosystemic shunt . - Used in investigation of hepatic encephalopathy .
Uses
Alone
- Hepatic encephalopathy.
Cats with suspected hepatic encephalopathy should NOT be further tested using ammonia tolerance test as this may be fatal. - Portosystemic shunt .
Bile acids are a better index of hepatic function.
In combination
- Liver failure.
- Ammonia tolerance test may be indicated if have capacity to run ammonia test rapidly and fasting ammonia is not elevated, or only minimally elevated. Do not challenge animal if fasting ammonia is significantly elevated!
Result data
Normal (reference) values
- Fasting level: <0-60 umol/l (<35 ug/dl).
- Conversion factor: ug/dl x 0.5872 → umol/l.
Abnormal values
Elevated levels:- Portosystemic shunt (decreased BUN) .
- Liver failure .
- Severe uremia .
Errors and Artifacts
- Non-EDTA anticoagulants may contain ammonium, giving falsely high results.
- Samples tested more than 2 hours after collection may have elevated levels due to breakdown of urea.
Sources
Publications
Other sources of information
- Ettinger S J & Feldman E C (eds) (2000) Textbook of Veterinary Internal Medicine. 5th edn. Philadelphia: W B Saunders & Co.
- Kaneko J J, Harvey J W & Brass M L (eds) (1997) Clinical Biochemistry of Domestic Animals. 5th edn. Boston: Academic Press.
- Duncan J R, Prasse K W & Mahaffey E A (1994) Veterinary Laboratory Medicine. Clinical Pathology. 3rd edn. Iowa: Iowa University Press.
