Bilirubin is a compound in the blood of dogs that is excreted in faeces and urine. The yellowish-brown substance is a by-product of the breakdown of heme in the blood. Heme is in the haemoglobin in the red blood cells and is responsible for carrying oxygen. The breakdown of heme is a normal part of the body recycling the red blood cells. After heme is broken down, the resulting Bilirubin is taken to the liver where it is processed into a water-soluble form that can be taken to the intestines and kidneys to be excreted.
Normal levels of bilirubin in a dog's urine are less than 1 milligram per decilitre (0.00001 oz/fl oz). Once the bilirubin reaches 2 mg/dl (0.00002 oz/fl oz), then the dog will become jaundiced, which is a yellowish colour of the skin and whites of the eyes. When this happens, the dog will need to be treated for the underlying cause of the elevated bilirubin. The causes for jaundice are found to be in three categories: pre-hepatic, hepatic and post-hepatic.
Pre-hepatic jaundice is caused by an excessive breakdown of red blood cells, which is called hemolysis, or by significant muscle injury. The injured muscle cells release heme, which is broken down into the extra bilirubin. Hemolysis results in anaemia. To treat this, the underlying cause for the anaemia must be found and treated. This can include anything from internal bleeding, to cancer, to infection.
Hepatic jaundice is caused by a disease or disorder of the liver. This can include an infection, which can be treated with antibiotics. Many liver diseases can only be managed through drugs, vitamins, or other supplements.
Post-hepatic jaundice is caused by a blockage in the bile duct or a leak in the biliary tract or by gallbladder disease. This is usually treated with the surgical removal of the blockage or the gallbladder, or the surgical repair of the leak. Pancreatitis can also cause a blockage in the bile duct and the blockage may go away on its own when the pancreatitis is treated.
Diagnosis of jaundice begins with a blood test. If the dog is anaemic, then the underlying cause for the anaemia must be found.
If the dog is not anaemic, then a chemistry analysis of the blood is done to check for other levels of enzymes and other compounds that could indicate liver disease or gallbladder disease.
The next step would be to take X-rays under anaesthesia to look for blockages or leaks or to check the condition and size of the liver and gallbladder. Ultrasound could also be used to check for blockages. A biopsy of the liver may be needed to check for liver disease.
If the cause is still not determined after all these steps, the last resort would be exploratory surgery to look for causes that didn't show up on X-rays or ultrasound.