Liver Function Tests

Liver Function Tests
Portal venous-systemic venous shunting of blood impairs delivery of portal substances to the liver. Shunting of this sort can occur as a result of congenital vascular anomalies, or secondary to chronic inflammatory disease with associated fibrosis. The decreased availability of normal hepatotrophic factors in portal blood leads to hepatic atrophy. Certain substances such as ammonia and bile acids are normally absorbed by the intestine and removed efficiently by hepatocytes after delivery from portal blood. Blood levels increase if portal blood bypasses the liver via shunts. The liver is essential for production of many substances in the body, including urea, coagulation factors, cholesterol and albumin. Decreased hepatic function (due to disease or shunts) can result in decreased production of these substances, producing a low urea, prolonged coagulation times, hypoalbuminemia and hypocholesterolemia. Each of these, however, can also be greatly affected by abnormalities outside the liver, rendering them unreliable as primary indicators of hepatic function. Therefore, hepatic function is assessed primarily by determination of ammonia and bile acids, especially the latter as it the most accessable test for the veterinary practitioner. Liver function can also be evaluated by the ability of the liver to clear exogenously administered compounds, such as ammonia (ammonia tolerance test), and dyes such as BSP and indocyanine green. These "challenge" tests are not performed on a routine basis.

Portal venous-systemic venous shunting of blood impairs delivery of portal substances to the liver. Shunting of this sort can occur as a result of congenital vascular anomalies, or secondary to chronic inflammatory disease with associated fibrosis. The decreased availability of normal hepatotrophic factors in portal blood leads to hepatic atrophy.
Certain substances such as ammonia and bile acids are normally absorbed by the intestine and removed efficiently by hepatocytes after delivery from portal blood. Blood levels increase if portal blood bypasses the liver via shunts.
The liver is essential for production of many substances in the body, including urea, coagulation factors, cholesterol and albumin. Decreased hepatic function (due to disease or shunts) can result in decreased production of these substances, producing a low urea, prolonged coagulation times, hypoalbuminemia and hypocholesterolemia. Each of these, however, can also be greatly affected by abnormalities outside the liver, rendering them unreliable as primary indicators of hepatic function.
Therefore, hepatic function is assessed primarily by determination of ammonia and bile acids, especially the latter as it the most accessable test for the veterinary practitioner. Liver function can also be evaluated by the ability of the liver to clear exogenously administered compounds, such as ammonia (ammonia tolerance test), and dyes such as BSP and indocyanine green. These "challenge" tests are not performed on a routine basis.