Final answer:
The presence of bilirubin in urine can confirm the diagnosis of a bile duct obstruction.
Step-by-step explanation:
The presence of bilirubin in urine can confirm the diagnosis of a bile duct obstruction in a cat. When there is a blockage in the flow of bile in the bile ducts, conjugated bilirubin, which is normally excreted in bile, cannot be properly eliminated and may appear in the bloodstream and urine. This condition, known as bile duct obstruction or post-hepatic jaundice, can be detected through tests such as the Van den Bergh test for jaundice or Gmelin's test for bile pigments. Therefore, the presence of bilirubin in urine can serve as a diagnostic marker for confirming a possible bile duct obstruction in the cat.