Bilirubin is a yellowish substance found in our bodies that is made when red blood cells break down. It is also what gives our skin and eyes a yellow color when there is a problem with the liver or gallbladder. Full definition
Cancers (eg lymphosarcoma) associated with the feline leukemia virus, the debility of feline AIDs or cats that have developed FIP can all suffer from high bilirubin levels as well. (2ndchance.info)