In staining techniques, in most cases bilirubin refers to the sum total of all types of bilirubin in the same reactive manner, which includes bound bilirubin, unconjugated bilirubin, bilirubin, bilirubin-like, etc., which have different chemical structures and different physical properties, especially their solubility in water and ethanol varies widely. Most liver tissue sections are a mixture of bilirubin, bound bilirubin and unconjugated bilirubin under the microscope, which is mostly seen in bile duct obstruction, bilirubin metabolism abnormality, hepatocyte necrosis or degeneration, etc. It is important to identify bilirubin and lipofuscin in liver histology, and it is not easy to distinguish between them as they both appear in yellowish-brown color in ordinary HE staining.