PAS diastase stain
PAS diastase is a histological stain often used by pathologists as an ancillary study in making a diagnosis on paraffin-embedded tissue samples. Diastase is an enzyme that breaks down glycogen and PAS is a stain that typically gives a magenta color in the presence of glycogen. When the two are used together a light pink color replaces the deep magenta. Differences in the intensities of the two stains (PAS and PAS-D) can be attributed to different glycogen concentrations and can be used to semiquantify glycogen in samples. In practice, the tissue is deparaffinized, the diastase incubates, and then the PAS stain is applied.
Histoplasma in a granuloma. PAS diastase stain.