A dog's liver has many responsibilities: breaking down toxins before they enter the body, removing waste products from the blood, storing energy and giving blood the ability to clot. While the liver is enormously resilient--it can continue to function even after large portions have been removed--the levels of enzymes present in this critical organ can serve as a gauge of your dog's overall health.
Five Key Enzymes
A typical liver blood panel run by a veterinarian returns values on enzymes, proteins and other things present in the liver. Of these values, those of five particular enzymes are most significant in reaching a diagnosis. If elevated beyond the normal values, they can indicate liver disease or failure.
The five enzymes are Alanine Aminotransferase (ALT), Aspartate Aminotransferase (AST), Alkaline Phosphatase (ALKP), Serum Bilirubin and Gamma Glutamyltransferase (GGT).
Normal Enzyme Levels
The normal enzyme levels listed below are taken from the Merck Veterinary Manual. Each value range is given in units per liter (u/L) or milligrams per deciliter (mg/dL).
ALT: 8.2 to 57 u/L
AST: 8.9 to 49 u/L
ALKP: 10.6 to 101 u/L
Serum Bilirubin: 0.1 to 0.6 mg/dL
GGT: 1.0 to 9.7 u/L
Symptoms of Liver Disease
A variety of symptoms are associated with liver disease. They can include such vague behavior as vomiting, diarrhea, fever and weight loss; more severe symptoms can include anorexia, gastric ulceration, impaired brain function, abnormal clotting, jaundice, build-up of fluid in the abdomen, producing abnormally large amounts of urine, excessive thirst, or an abnormally enlarged liver or abnormally small liver. These severe symptoms often occur in the later stages of liver disease, making early diagnosis even more critical, especially since enzyme levels may normalize at the end of the disease.
The Merck Veterinary Manual lists signs of impaired brain function because of liver disease as "circling, head pressing, aimless wandering, weakness, ataxia [unsteady or staggering movement], blindness, ptyalism [excessive saliva], aggression, dementia, seizures and coma."
Your Dog's Normal Levels
Especially as your dog ages, it's important to know its normal liver enzyme levels. Many veterinarians have comprehensive "senior panels" that they can run on your pet, which will include liver enzymes. The value is in being able to compare the levels in a healthy pet to those of one developing liver disease. If your dog is consistently on the lower end of the scale, it might be significant to find numbers suddenly at the high end. Early diagnosis and treatment, regardless of your dog's age, is critical.
If your dog develops liver disease, your vet will likely want to work with you toward finding an underlying cause. While liver disease can develop on its own, it's worth discovering the root of the problem rather than simply treating the symptoms. Balancing electrolytes and acids and bases is common treatment, as is nutrition appropriate for your dog's symptoms. When no other cause can be found, treatment focuses on slowing the disease and keeping complications under control.