the next diagnostic step to help differentiate between hepatic and post-hepatic icterus. If the common bile duct is >5mm, extrahepatic biliary duct obstruction (EHBDO) is likely. Causes of EHBDO include choleliths, neoplasia, flukes, cholangitis, and pancreatitis.
ICTERIC CATS:
More Than Just Hepatic Lipidosis
Ultrasound of an icteric cat with a severely dilated and tortuous bile duct from an extrahepatic bile duct obstruction.
Image courtesy of Dr. Adam Honeckman
Adam Honeckman | DVM, DACVIM (Small Animal Internal Medicine)
Icterus can be defined as increased bilirubin in the serum, urine, or tissues. Bilirubinuria can be detected earlier than hyperbilirubinemia. Often, serum total bilirubin concentration must exceed 3 mg/dl before it can be detected on physical exam, whereas a serum bilirubin of >1mg/dl can cause the serum to be grossly icteric.
Veterinary Specialty Solutions
Bilirubin is a product of hemoglobin metabolism. Increased levels can occur due to prehepatic (hemolysis), hepatic, or post-hepatic causes. With the exception of Mycoplasma haemofelis (formerly known as Hemobartonella felis), hemolytic anemias are relatively uncommon in cats. Most causes of icterus in cats are hepatic or post-hepatic in origin. Although hepatic lipidosis is reported to be one of the most common causes of icterus in cats, several other differentials need to be considered. A review of 50 icteric cats seen in the author's practice revealed that only 30% had hepatic lipidosis. Cholangitis was responsible for 20%, and lymphoma was diagnosed in another 20%. Pancreatitis (15%), extrahepatic bile duct obstruction (10%), and other miscellaneous diseases (5%) were responsible for the remaining icteric cats. The disease could also have more than one identifiable cause (i.e., hepatic lipidosis + cholangitis and/or pancreatitis, pancreatitis + cholangitis +/- inflammatory bowel disease).
In cases of pancreatitis, abdominal ultrasonography may reveal an enlarged hypoechoic pancreas surrounded by hyperechoic fat, pancreatic duct dilation, and/or localized peritoneal effusion. A normal ultrasound doesn’t rule out pancreatitis since the sensitivity is only about 11-84%. A fasted spec fPL (run by Texas A&M GI laboratory or Idexx) is the most sensitive and specific test for feline pancreatitis. Alternatively, the PSL assay by Antech has been shown to have a fair correlation with the spec fPL in some studies. The author prefers to use both abdominal ultrasound and the spec fPL (or PSL) to diagnose pancreatitis. The snap fPL test is a screening test (a negative test makes pancreatitis less likely), but a positive test is nonspecific and needs to be confirmed by abdominal ultrasound and/or spec fPL determination. If abdominal ultrasound does not demonstrate changes consistent with pancreatitis or EHBDO, hepatic icterus is most likely. A diffusely hyperechoic liver is highly suggestive of hepatic lipidosis but can also be seen in diabetic or healthy obese cats. The ultrasound appearance of lymphoma or cholangitis can be variable, sometimes with no abnormalities being found.
LIVER FINE NEEDLE ASPIRATE VS. BIOPSY Cytology or histopathology is needed for a definitive diagnosis of hepatic icterus because ultrasound changes of hepatic parenchyma are often nonspecific. Cytologic evaluation of liver fine needle aspirates may be useful in diagnosing hepatic lipidosis or lymphoma, but often misses necroinflammatory disorders such as cholangitis. Therefore, histopathologic evaluation of a liver biopsy may be superior to a fine needle aspirate.
Image courtesy of Canva.
DIAGNOSTIC EVALUATION When evaluating an icteric cat, the PCV should be assessed. If the PCV <20%, then pre-hepatic causes are most likely. The exception would be in cats with anemia, and icterus due to simultaneous involvement of the bone marrow and liver (i.e., lymphoma or other myeloproliferative disease). If the PCV >20%, then hemolytic anemia is unlikely, and the diagnostics should focus on hepatic and post-hepatic causes of icterus. If hemolytic diseases are ruled out, abdominal ultrasonography is
Fine needle aspirate from a liver of an icteric cat containing a large number of lymphoblasts diagnostic for large cell lymphoma.
Image courtesy of Dr. Adam Honeckman
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