Periodic Acid Schiff (PAS)

November 11, 2023

Periodic acid Schiff (also known as PAS) is a special stain test performed by pathologists to look for two types of chemicals in a tissue sample: a type of sugar called glycogen, and a type of protein called mucin. Pathologists often perform a PAS stain when they are trying to determine if the cells in the tissue sample are producing glycogen or mucin. Pathologists also sometimes use PAS to look for fungal micro-organisms such as Candida or Pneumocystis. When a PAS-stained slide is examined under the microscope, both glycogen and mucin appear bright pink or red. Fungal micro-organisms will also appear bright pink or red. This test is often performed at the same time as a periodic acid Schiff plus diastase (PAS-D) stained slide. PAS-D is very similar to PAS except for an added chemical called diastase. Diastase breaks down glycogen which makes it easier to see mucin.

About this article

This article was written by doctors to help you read and understand your pathology report. Contact us if you have questions about this article or your pathology report. For a complete introduction to your pathology report, read this article.

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