This article is one in a continuing series which describes diagnostic tests performed by the avian vet. In this column, I would like to finish discussing some of the other parameters that are evaluated on a blood chemistry panel. Bilirubin is formed in the liver from the breakdown of aged red blood cells. When excess bilirubin is present as a result of the diseased liver's inability to handle it, it becomes deposited in the tissues, leading to a yellowing known as icterus or jaundice.
Birds lack the enzyme necessary to form bilirubin and thus form biliverdin instead.
Biliverdinuria, or the deposition of greenish pigments in the urine, occurs instead of jaundice in birds with liver disease. In the past it has been very difficult to evaluate liver function in birds. The enzymes traditionally used were not liver specific and became elevated for many different reasons in addition to liver disease. The advantage is that is is liver specific and therefore is a very good indicator of liver function. Bile acids are formed in the liver from cholesterol and are excreted in the intestine where they assist in the digestion of lipids.