PASD Special Stain - Periodic Acid-Schiff with Diastase (PASD) Special Stain

PAS staining with digestion (PASD) is a modification of traditional PAS (periodic acid Schiff) staining. In this method, one of the identical tissue slides is first treated with the enzyme diastase, which selectively breaks down and dissolves glycogen. Both the diastase-treated slide and the untreated slide are then stained with PAS stain. The staining of the two is compared: any substance that appears colored in the untreated slide but disappears in the treated slide is identified as glycogen. Substances that remain colored in both are mucosal substances other than glycogen.