PAS fungal stain; fast green counterstain
The periodic acid-Schiff (PAS) staining procedure is most commonly used in the histology laboratory to detect glycogen deposits in the liver when glycogen storage disease is suspected. Glycogen granules may also be visible in tumors of the bladder, kidney, ovary, pancreas, and lung.
Basement membranes, which are present in various tissues in the body, may also be visualized through the PAS staining procedure. The PAS is most commonly used to demonstrate the thickness of glomerular basement membrane when renal disease is being assessed.
The PAS staining procedure is also used to demonstrate hyphae and yeast-forms of fungi in tissue samples due to the high carbohydrate content of the organism's cell walls. Common fungal species that are PAS reactive are Candida albicans, Aspergillus fumigatus, and Cryptococcus neoformans.
Neutral mucins in the gastrointestinal tract and some epithelial mucins will also give a PAS-positive staining reaction.