Bilestaining

Bilestaining is a histochemical stain used to detect bile pigments, such as bilirubin and biliverdin, within fixed tissue sections. By visualizing bile pigments, pathologists can assess the distribution and relative burden of pigment deposition in liver, biliary ducts, and related structures, aiding in the evaluation of cholestasis and liver disease.

The most commonly described approach is Fouchet's staining. In this method, tissue sections are treated with Fouchet's reagent, a mixture that promotes oxidation of bile pigments and yields a distinctive color in pigment-containing areas. Bilirubin typically appears green, whereas biliverdin can give a blue-green hue. Some protocols combine Fouchet's stain with a counterstain (for example hematoxylin) to provide tissue context.

Interpretation relies on color, location, and comparison with controls. Positive staining for bilirubin is typically seen in hepatocytes near canaliculi, bile ducts, and areas of pigment accumulation. The technique is used to investigate cholestatic patterns, biliary obstruction, and pigment retention.

Limitations include imperfect specificity, as other compounds or pigments can produce similar colors under certain conditions. The method is sensitive to fixation, dehydration, and reagent freshness, and staining can fade over time. Because of these issues and the availability of more selective or quantitative methods, bilestaining is mainly of historic or supplementary value today rather than a routine primary diagnostic test.