Certain factors make it is very difficult to diagnose liver disease in dogs.
* Symptoms of liver disease in dogs are difficult to pin point as they are subtle and vague and often mimic those relating to other diseases.
* Liver cells can continue to perform their dedicated functions despite the liver mass being affected.
* The liver has a great reserve capacity.
* The liver can be affected by other diseases as it supports and is supported by many other organs and systems in the body.
All these factors can lead to frustration for a veterinarian to diagnose whether the liver is affected and to what extent. One of the tools that the specialist will use is to get a complete chemistry profile of a blood sample.
Although, clinical pathological tests and enzymology play a crucial role in arriving at correct diagnoses, it seldom indicates any deviation from a healthy condition of the liver. Enzymology is a branch of biochemistry that deals with the chemical nature and biological activity of enzymes.
Another factor that complicates diagnosis of liver disease is that the levels of even enzymes that are specific to liver can be disturbed by secondary hepatic disease also.
ALT (alanine aminotransferase) or SGPT (serum glutamic pyruvic transaminase) is a liver specific enzyme. It is concentrated in the cytosol and is released when localized liver cells die from infection or the interruption of blood supply. Serum levels increase two to three days after the liver has been affected and return to normal after a couple of weeks of treatment.
Generally, two to three times the normal level is considered as insignificant and only a persistent increase is considered to be abnormal. ALT levels may go up to four to five time the normal level even in non-hepatic disorders like inflammation of the gastrointestinal tract, hemolytic anemia and heart failure. A dog undergoing treatment with anticonvulsants and glucosteroids or those that have an inhibited flow of bile may also show a moderate increase in ALT levels.
AST (Aspartate aminotransferase) or SGOT (serum glutamic oxaloacetic transaminase) is another liver enzyme, also found in muscle tissue and red blood cells. An increase in levels of AST indicates a more severe liver disease than ALT.
SAP (Serum alkaline phosphatase) levels increase in certain forms of cancers including liver cancer. Elevated levels of SAP are more significant in cases of feline liver disease than in dogs.
GGT (Gamma-glutamyl transpeptidase) levels signify liver disease caused by blockage of bile ducts.
Vague symptoms of liver disease in dogs like diarrhea, vomiting and anorexia are often misread as relating to indigestion and other mild ailments.
Symptoms like jaundice, which are specific usually surface at a later stage of liver disease. In such a situation, despite the confusion over reading the results of laboratory tests and the accompanying emzymology, a complete chemistry profile is of utmost necessity to diagnose liver disease in dogs.