A yellow discoloration visible on your cat’s paws or skin is a clinical sign known as icterus or jaundice, signaling a serious underlying medical problem that requires immediate veterinary attention promptly. This yellowing is most easily observed in areas with less fur, such as the inner ear flap, the gums, the whites of the eyes (sclera), and the paw pads. The presence of this symptom means a yellow pigment is accumulating in your cat’s tissues.
Understanding Jaundice and Bilirubin
The yellow pigment responsible for this discoloration is called bilirubin, and its excessive buildup in the bloodstream is termed hyperbilirubinemia. Bilirubin is a naturally occurring waste product, primarily formed when the body breaks down old or damaged red blood cells. The hemoglobin molecule within these cells is metabolized, and the resulting heme component is converted into bilirubin.
This unconjugated bilirubin is released into the bloodstream and travels to the liver. Liver cells take up the pigment and chemically alter it through conjugation, making it water-soluble so it can be excreted. This conjugated bilirubin is then secreted as a component of bile, traveling through the bile ducts and into the intestines to be eliminated in the stool. When this system of production, processing, or excretion is disrupted, bilirubin backs up into the circulation and causes visible yellowing.
Primary Medical Causes of Yellowing
Medical causes of bilirubin buildup are categorized into three groups based on where the problem occurs along the metabolic pathway. These are pre-hepatic, hepatic, and post-hepatic conditions, indicating whether the issue is before, within, or after the liver. Jaundice becomes visible when there is a significant failure in one of these three stages.
Pre-Hepatic Causes
Pre-hepatic jaundice occurs when red blood cells are destroyed too rapidly, overwhelming the liver’s ability to process the sudden increase in bilirubin production. This rapid destruction of red blood cells is known as hemolysis, and it often leads to severe anemia. Infectious agents, such as the blood parasite Mycoplasma haemofelis, are common triggers for this type of red blood cell damage.
Hepatic Causes
Hepatic jaundice involves diseases that directly damage the liver cells, impairing their ability to take up, conjugate, or secrete bilirubin. The most frequent cause of severe hepatic jaundice in cats is Feline Hepatic Lipidosis, commonly known as fatty liver disease.
This condition occurs when fat accumulates excessively in the liver cells, often following a period of anorexia or rapid weight loss, preventing normal liver function. Other causes include cholangiohepatitis, which is inflammation of the liver and bile ducts, as well as cancers like lymphoma or viral infections such as Feline Infectious Peritonitis (FIP).
Post-Hepatic Causes
Post-hepatic jaundice results from an obstruction that physically blocks the flow of bile out of the liver and into the small intestine. This blockage causes conjugated bilirubin to back up into the bloodstream, leading to very high concentrations.
Pancreatitis, or inflammation of the pancreas, is a common cause because the swollen pancreas can compress the common bile duct, which runs nearby. Other obstructions may be caused by gallstones (choleliths), tumors, or severe inflammatory tissue within the bile duct system.
Immediate Steps and Veterinary Examination
Noticing a yellow tint on your cat’s skin or paws should prompt an urgent call to your veterinarian. The initial veterinary workup focuses on determining which of the three categories—pre-hepatic, hepatic, or post-hepatic—is the root cause of the hyperbilirubinemia.
The diagnostic process begins with a complete blood count (CBC) and a full serum chemistry panel. The CBC helps identify if red blood cell destruction (hemolysis) is occurring, while the chemistry panel measures bilirubin levels and assesses liver enzyme activity. A urinalysis is also typically performed, as the presence of bilirubin in the urine is considered a significant finding in cats.
Diagnostic imaging is usually the next step, with an abdominal ultrasound being the most informative tool. The ultrasound allows the veterinarian to visualize the liver structure, assess the gallbladder, and check for physical blockages or dilation of the bile ducts. This imaging is often required to distinguish between liver disease and an extrahepatic biliary obstruction, which often requires surgical intervention.