What is icterus?
Icterus is also known as jaundice or yellow jaundice. It refers to an excessive accumulation of a yellow pigment in the blood and tissues. When icterus has been present for any length of time, it will discolor many tissues and will become visible as jaundice on most body surfaces, including the skin. It is most easily seen in the gingivae (gums), the sclerae (white part of the eyes), and the pinnae (ear flaps). Jaundice may be difficult to detect in dogs that have pigmented (dark) gums or skin.
What causes icterus?
The causes of icterus fall into three major categories:
- Destruction of red blood cells. The process of red cell destruction is known as hemolysis. It can occur within blood vessels (intravascular hemolysis) or in the spleen and liver (extravascular hemolysis). Hemolysis causes a type of anemia called hemolytic anemia, which is different from blood loss anemia that is a result of bleeding from an injury.
- Liver disease. Any disease or condition that damages or destroys liver cells can cause icterus.
- Obstruction of the bile duct. Bile is stored in the gall bladder and transported into the small intestine by the bile duct. If bile becomes abnormally thick, if gallstones form in the gall bladder, if the gall bladder or bile ducts become inflamed, or if the liver becomes swollen so that the bile ducts are constricted, bile flow will become obstructed.
How is the cause of icterus diagnosed?
The diagnosis of icterus is usually straightforward by means of a physical examination. Occasionally, a blood sample is drawn from a dog for some other reason and the serum is noted to be yellow before the dog becomes visibly jaundiced. In these cases, the yellow serum is usually an indication of impending problems, and your veterinarian will recommend a complete diagnostic work-up.
Determining the reason for the icterus can be a challenge and requires a systematic approach. There are several potential causes for icterus within each category listed above; the first step is to perform screening tests to determine which of the three categories is involved and to narrow down the list of likely diseases. Based on the preliminary tests, your veterinarian will perform additional tests to determine the cause of icterus in your dog.
How is hemolysis diagnosed?
Your veterinarian will perform a test called a complete blood count (CBC). The CBC measures the number of red blood cells, white blood cells, and platelets (important for normal blood clotting). If an automated machine is used to perform the CBC, the red blood cells will be measured by a direct red blood cell count. As part of the CBC, tests called the packed cell volume (PCV) and/or the hematocrit will determine the proportion of the blood that is red blood cells. These measurements will indicate whether the dog is anemic. Other components of the CBC will help determine whether the anemia is caused by hemolysis, including an examination of a blood smear to look for immature red blood cells, abnormal red blood cells, or unusual clumping of cells.
What causes hemolysis?
Hemolysis can be caused by toxic plants, drugs, parasites on the red blood cells, heartworm disease, autoimmune diseases, and cancer. Several additional tests may be needed to determine the cause of hemolysis in your dog.
How is liver disease determined to be the cause of jaundice?
A biochemistry profile, which is a group of 10-30 tests, is performed on a blood sample from the dog with icterus. The biochemistry profile contains several tests that are specific for liver disease and some that are supportive of liver disease. The main ones are alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP or ALKP), and total bilirubin. In some cases, your veterinarian will also recommend a bile acid analysis, which assesses liver function.
"These blood tests will indicate that liver disease is present, but not its cause or whether it is reversible."
These blood tests will indicate that liver disease is present, but not its cause or whether it is reversible. To make that determination, a biopsy of the liver is often necessary. This can be done in three ways:
- Fine-needle aspiration. To perform this procedure, a small gauge needle attached to a syringe is inserted through the skin into the liver, and cells are withdrawn or aspirated. The cells are placed on a glass slide, stained, and studied under a microscope by a veterinary pathologist. This is the least invasive and quickest test, but it has certain limitations. Because only a few cells are obtained, it is possible that a representative sample from the liver will not be obtained. It is also not possible to view the cells in their normal relationship to each other.
- Needle biopsy. This procedure is similar to the fine needle aspiration except a much larger needle is used. For this technique, your dog will require either heavy sedation or general anesthesia. The needle biopsy gives a core of liver tissue, not just a few cells. The sample is fixed in formaldehyde and submitted to a pathology lab for analysis (a technique called histopathology). The core biopsy allows the pathologist to view the cells in their normal relationship to each other. Often, this test is performed during an ultrasound examination and is called an ultrasound-guided needle biopsy.
- Surgical wedge biopsy. The dog is placed under general anesthesia, and the abdomen is opened This permits direct observation of the liver and the surgeon chooses the exact site for biopsy. A piece of the liver is surgically removed using a scalpel. This approach gives the most reliable biopsy sample.
What types of liver disease cause icterus?
The most common causes of liver disease include viral or bacterial infections, ingestion of toxic plants or chemicals, certain drugs and medications, cancer, autoimmune diseases, and certain breed-specific liver diseases.
What tests determine bile duct obstruction?
Dogs with obstructed bile ducts are usually extremely icteric. In addition to the discoloration in the whites of the eyes and the gums, their skin is usually an obvious yellow color. The gall bladder and bile duct must be examined to confirm the presence of an obstruction.
"An ultrasound examination is a more accurate non-invasive technique
to evaluate the gall bladder and bile duct."
Although this may be possible using radiographs (X-rays), an ultrasound examination is a more accurate non-invasive technique to evaluate the gall bladder and bile duct. Sometimes, exploratory surgery is necessary to properly evaluate the dog for biliary obstruction or gallstones.
What causes bile duct obstruction?
The most common causes of bile duct obstruction in dogs include pancreatitis, abdominal trauma, abdominal or liver cancer, gall bladder stones (gallstones), and severely thickened bile.
How is icterus treated?
Icterus is not a disease; it is a clinical sign indicating that an underlying disease is present. When the underlying disease is diagnosed and treated successfully, the icterus will resolve.
What is the prognosis for my dog's recovery?
The prognosis depends upon the underlying cause. Some diseases that cause icterus are ultimately fatal, such as cancer, while others are treatable, with a good prognosis for full recovery.