Cats are experts at hiding even very serious illnesses. At the Animal Clinic at Thorndale, we understand that owners may not always recognize subtle changes in our cats that are occurring over time. How often do owners actually look in their cat’s mouths? How often to you part your cat’s fur to look at the skin beneath? Icterus, the yellowing of the skin and mucous membranes, develops over time, and is most commonly due to the break down of red blood cells inside the blood stream, liver disease or bile duct obstruction.

Icterus

Icterus is also known as jaundice or yellow jaundice. It means that a yellow pigment is found in the blood and in the tissues. In an icteric cat, the yellow coloration is most easily seen in the gums, the sclerae (white part of the eyes), the skin between the ears and the eyes, and the pinnae (ear flaps). However, if these tissues normally have a dark color, icterus may not be visible.

Contributing Factors

Icterus is often associated with the presence of fleas or ticks, infection with feline leukemia virus, feline infectious peritonitis, travel to areas endemic for liver flukes or fungal diseases, prolonged anorexia, ingestion of drugs or toxins, and presence of immune-mediated diseases. It can also be seen in diabetes mellitus in cats

Clinical Signs

A yellow color is noted in the skin, white part of the eyes, or on the ear flaps.

Causes

The causes of icterus fall into three major categories:

1. Destruction of red blood cells. This can occur within blood vessels (intravascular) or in the spleen and liver (extravascular). The process of red cell destruction is known as hemolysis.
2. Liver disease. Any disease that causes destruction of liver cells or causes bile to become trapped in the liver can cause icterus.
3. Obstruction of the bile duct. The bile duct carries bile, an important fluid for digestion, from the gall bladder to the small intestine. Obstruction can occur within the gall bladder or anywhere along the bile duct.

Diagnosis

The diagnosis of icterus itself is straightforward; the yellow color is detected in tissues or blood. However, determining the cause of icterus can be a challenge and usually requires a series of tests. Within each category listed above are several possible causes of icterus. Once the probable cause can be placed into one of these three categories, additional tests are performed to look for a specific disease that is leading to the icteric state.

Occasionally, blood is drawn and the serum component is found to be icteric before the cat is visibly jaundiced. This information is helpful and can give a clue to impending problems.

Hemolysis

Since hemolysis results in destruction of red blood cells (erythrocytes), determination of red blood cell numbers is one of the first tests performed on the icteric patient. There are three tests that may be used for this. The red blood cell count is an actual machine count of red blood cells. The packed cell volume (PCV) is a centrifuge-performed test that separates the red blood cells from the serum or plasma (the liquid parts of the blood). The hematocrit is another way to determine if there is a reduced number of red blood cells. It is a calculated value that is essentially identical to the PCV. All three of these tests are part of a complete blood count (CBC).

Hemolysis can be caused by toxic plants, chemicals, drugs, parasites on the red blood cells, heartworms, autoimmune diseases, and cancer. Several tests are needed to determine which of these is the cause. Visually examining a droplet of the cat’s blood under the microscope can help in the diagnosis. In some immune mediated diseases, the red cells clump together. With certain toxins, the color of the red cells change. Blood parasites may be identified on a blood smear and unusual shapes of red cells can be observed, indicating certain types of damage to the cells.

Liver Disease

A chemistry profile is performed on pets with icterus. This is a group of 20-30 tests that are performed on a blood sample. The chemistry profile contains several tests that are specific for liver disease. The main ones are the alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP), albumin, and total bilirubin. If these tests are normal yet there is reason to suspect liver disease, a bile acid analysis may be performed.

Although each of these tests is used to “look” at the liver from a slightly different perspective, ultimately they only determine that liver disease is present. None of them are able to determine the exact cause of the disease. An abdominal ultrasound is usually performed once liver disease is suspected. This allows examination of the liver and bile duct structure. The liver may be biopsied or a sample of cell taken to get a definitive diagnosis. This can be achieved several ways:

1. Fine-needle aspirate. To perform this procedure, 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 (ie., tissue architecture). Some diseases can be diagnosed with this technique, and others cannot.
2. Large needle biopsy. This procedure is similar to the fine-needle biopsy except a much larger needle is used. This needle is able to recover a core of tissue, not just a few cells. The sample is fixed in formaldehyde and submitted to a pathologist for analysis. General anesthesia is required, but the cat is anesthetized for only a very short time. Ultrasound guidance of the biopsy needle is highly desirable to minimize complications. If it is done properly and with a little luck, this procedure will recover a very meaningful sample. However, the veterinarian cannot always choose the exact site of the liver to biopsy. Therefore, it is still possible to miss the abnormal tissue. The most significant difficulty with this technique is the inability to control hemorrhage from the biopsy site.
3. Fine-needle biopsy. This is a relatively new technique that is a combination of the fine needle aspiration and the large needle biopsy. A small needle is used to collect the sample. However, aspiration is not used. Short anesthesia and ultrasound guidance are required to choose the biopsy site and to increase safety. The tissue sample is smaller than the large needle biopsy but much greater than the needle aspirate. A cytopathologist can generally give a very good interpretation. This technique has much less likelihood of bleeding difficulties than the large needle biopsy.
4. Surgical wedge biopsy. The cat is placed under general anesthesia, and the abdomen is opened surgically. This permits direct visualization of the liver so the exact site for biopsy can be chosen. A piece of the liver is surgically removed using a scalpel. This approach gives the most reliable biopsy sample, but the stress of surgery and the expense are the greatest of all of the biopsy methods. Bleeding from the biopsy site is a potential complication from this procedure so coagulation tests are often performed prior to needle biopsy or surgical biopsy.

Some of the causes of liver-related icterus include infectious diseases (feline leukemia virus, feline infectious peritonitis, fungal diseases), neoplasia, hepatic lipidosis (fatty liver), and cholangiohepatitis complex.

Bile Duct Obstruction

Pets with obstructed bile ducts are usually extremely jaundiced. Their yellow color can often be seen readily in the skin, as well as the sclerae and gingiva. However, an evaluation of the gall bladder and bile ducts is necessary to be sure that obstruction is present.

An ultrasound examination is the most accurate and non-invasive way to evaluate the gall bladder and bile duct. This technology uses sound waves to “look” at the liver, gall bladder, and bile duct. If this is not available, radiographs (x-rays) should be taken of the liver. However, exploratory surgery may be necessary to be properly evaluate the pet for biliary obstruction.

The most common causes of bile duct obstruction include pancreatitis, trauma, cancer, gall bladder stones, liver flukes, and severely thickened bile.

Treatment

Icterus is not a disease; it is a sign that disease is present. Therefore, there is not a specific treatment for icterus. Icterus will resolve when the disease that causes it is cured.

The basis for resolving icterus is to diagnose the underlying disease. When the proper testing is done, this is usually possible. Then, treatment can begin.

Prognosis

The prognosis is dependent upon the underlying cause.