Ron Hines DVM PhD

The Ammonia Level In Your Pet’s Blood

Determining the blood ammonia level of your dog or of your cat is not a common frontline blood test. It is also a difficult test to run successfully. But if your dog or cat is showing marked personality changes, a blood ammonia level assay is one that your veterinarian might suggest.

Perhaps your pet has begun to lose some of its prior training. Perhaps it is becoming more forgetful, more confused, or it has lost some of its hygienic habits (potty training). If it is an elderly pet, cognitive dysfunction (aka pet dementia) might be on you or your vet’s mind. Perhaps it is a younger pet that is experiencing similar problems or has had a sudden personality change.

There are no specific blood tests for dementia. There are many possible causes that need to be ruled out one by one; and higher than normal blood ammonia levels related to liver disease is one of them.

The reason that the test is difficult to run accurately is that blood ammonia levels are unstable in blood samples. Ammonia is very volatile and quickly escapes from the sample. In the past, some veterinarians preferred the ammonia tolerance test where a known amount of ammonia was administered rectally. (read here)  However, the ammonia tolerance test in itself has been known to cause severe neurological reactions. I know of no one using it today. 

Health Problems That Might Cause Too Much Ammonia (hyperammonemia) To Be Present In Your Dog Or Cat’s Blood:

Your pet’s liver converts the ammonia produced during metabolism into less toxic urea. That is the BUN you see in your pet’s lab report. So, the health issues that cause a rise in blood ammonia level all relate to issues that are affecting your pet’s liver function. Those issues include Hepatic Encephalopathy, and other assorted liver problems. Circulatory defects such as Portosystemic Shunts that your pet was born with or, on rare occasion, developed due to some traumatic injury.  Failing kidneys on occasion are associated with increases in blood ammonia. That is not a constant finding and no explanation has been found. Inherited metabolic disorders that affect the processing of amino acids and possibly – excessively high-protein diets in specific genetically susceptible dogs and cats have also been reported. 

Delays in processing your pet’s blood sample after it was collected, collection issues such as hemolysis during blood collection or blood samples sitting too long at room temperature can also result in falsely elevated blood ammonia reading as urea slowly breaks down into ammonia.

Some cats that have developed an arginine deficiency due to malnutrition or not eating have also been found to have elevated blood ammonia levels. (ask me for Center2005.pdf)

Health Problems That Can Cause Too Little Ammonia To Be Present In Your Pet’s Blood:

I know of none.

Complementary tests:

Blood tests for evidence of liver disease. Elevated Bile acids is a more accurate way to detect portosystemic shunts than liver panel results.  Liver ultrasound.    Liver biopsy.  A trial on a low protein diet to see if your pet’s mentation improves.  Repeating the ammonia test at a different veterinary laboratory is another thing to consider.

DxMe

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