What is icterus?
Icterus is also known as jaundice or yellow jaundice. It refers to an excessive accumulation of a yellow pigment called bilirubin in the blood and tissues. Bilirubin is a breakdown product of hemoglobin, the protein in red blood cells that carries oxygen to the tissues.
Bilirubin should be removed from the bloodstream by the liver and then eliminated into the intestinal tract through the bile. If this process is not happening as it should, then bilirubin levels rise in the blood and urine. When icterus is present for any length of time, it will discolor tissues and become visible as jaundice on most body surfaces, including the skin.
Since most of a cat's skin is covered by fur, jaundice 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 cats 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 hemolytic anemia, which is different from blood loss anemia—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 icterus diagnosed?
Icterus is usually straightforward to diagnose through a physical examination. Occasionally, a blood sample is taken for some other reason and the serum (liquid portion of the blood) is noted to be yellow before the cat becomes visibly jaundiced. Yellow serum is an indication of impending problems, and your veterinarian will recommend a complete diagnostic work-up.
Determining the cause of icterus can be a challenge and requires a systematic approach. There are several potential causes for icterus within each category listed above, so the first step is to perform screening tests to determine which of the three categories is involved and 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 cat.
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). A low red blood cell count indicates your cat 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 toxins, drugs, parasites on the red blood cells, heartworm disease, infections, autoimmune diseases, and cancer. Several additional tests may be needed to determine which of these is causing the hemolysis and resulting icterus in your cat.
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 cat with icterus. The biochemistry profile contains several tests that are specific for liver disease.
The main liver enzymes are alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP), 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. Additional testing for infectious diseases may be recommended, depending on prevalence in your area. To make a definitive diagnosis, a biopsy of the liver is often necessary.
The biopsy can be done in one of three ways:
1. Fine needle aspiration. A small-gauge needle is inserted through the skin into the liver. A syringe is used to aspirate some cells from the liver. The cells are placed on a glass slide, stained, and studied under a microscope. 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.
2. Needle core biopsy. This procedure is similar to the fine needle aspiration except a larger biopsy needle is used. Often, this test is performed during an ultrasound examination and is called an ultrasound-guided needle biopsy. The needle biopsy gives a core of tissue, not just a few cells. The sample is fixed in formaldehyde and submitted to a pathologist for analysis (a technique called histopathology). General anesthesia is required, but your cat is anesthetized for only a very short time. The core biopsy allows the pathologist to view the cells in their normal relationship to each other. However, the veterinarian cannot choose the exact site of the liver to biopsy because the liver is not visible. Therefore, it is still possible to miss the abnormal tissue.
3. Surgical wedge biopsy. The cat is placed under general anesthesia and the abdomen is opened surgically, allowing the surgeon to see the liver and choose the exact site for biopsy. A piece of the liver is surgically removed using a scalpel. This approach gives the most reliable biopsy sample. Laparoscopic surgery may also be considered to obtain biopsy samples, using small incisions and specialized instruments.
What types of liver disease cause icterus?
Some of the causes of liver-related icterus include infectious diseases (feline leukemia virus (FeLV), feline infectious peritonitis (FIP), fungal diseases), neoplasia or cancer, hepatic lipidosis (fatty liver syndrome), and cholangiohepatitis complex.
How is bile duct obstruction determined?
Cats with obstructed bile ducts are usually extremely icteric. In addition to the discoloration in the whites of the eyes and gums, their skin is usually an obvious yellow color.The gall bladder and bile ducts must be examined to confirm the presence of an obstruction. Although this may be possible using radiographs (X-rays), an ultrasound examination is a more accurate, non-invasive way to evaluate the gall bladder and bile duct. Exploratory surgery is occasionally necessary to properly evaluate the cat for biliary obstruction.
What causes a bile duct obstruction?
The most common causes of bile duct obstruction in cats include pancreatitis, abdominal trauma, abdominal or liver cancer, gall bladder stones (gallstones), liver flukes, 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, icterus will resolve.
Will my cat recover?
The prognosis depends on the underlying cause. Some diseases causing icterus are fatal, but others have a good prognosis for full recovery.
