Trichrome

Trichrome, meaning "three colour" was used as the name of a staining method (Mallory's trichrome) which differentially coloured erythrocytes orange, muscle red and collagen blue.

It now has become a general term to describe any histological staining method which uses two or more acid dyes in conjunction with a "polyacid" to differentially stain two basic materials in contrasting colours. The most common application is to stain muscle fibres red and collagen fibres green or blue, Masson's trichrome being the most commonly used method. This is necessary since smooth muscle fibres may be difficult to differentiate from collagen. In addition, liver biopsies may have fine collagen fibres between the liver cells, and the amount of collagen may be estimated based on the staining method. Trichrome methods are now used for differentiating muscle from collagen, pituitary alpha cells from beta cells, fibrin from collagen, and mitochondria in fresh frozen muscle sections, among other applications. It helps in identifying increases in collagenous tissue (i.e. fibrotic changes) such as in liver cirrhosis and distinguishing tumours arising from muscle cells and fibroblasts.