Periodic acid Schiff plus diastase (PAS-D)

November 11, 2023


Periodic acid Schiff plus diastase (also known as PAS-D) is a special stain with various uses by pathologists. It is typically used in combination with the routine hematoxylin and eosin (H&E) stained slide.

Common uses for PAS-D include:

  • Intracellular mucin: PAS-D can help a pathologist differentiate between glycogen and mucin. When a PAS-D-stained slide is examined under the microscope, intracellular mucin (mucin inside of the cell) appears bright pink or red. In contrast, glycogen (which can look very similar to mucin on the routine H&E stained slide) looks white. Intracellular mucin is commonly found in a type of cancer called adenocarcinoma and this stain can help pathologists tell the difference between adenocarcinoma and other types of cancer that do not show intracellular mucin.
  • Fungal infections: This test makes it easy for pathologists to see fungal micro-organisms such as Candida and Pneumocystis because the PAS-D makes them look bright pink or red when examined under the microscope.
  • Whipple’s disease: Whipple’s disease is caused by infection with the bacteria T. whipplei. Pathologists will perform a PAS-D test on tissue samples from the small bowel in patients who may have Whipple’s disease. This test makes it easier to see specialized immune cells called histiocytes which are found in large numbers in Whipple’s disease.
  • Liver disease: The PAS-D test can be used to highlight an abnormal protein called alpha-1-anti-trypsin in the liver. Alpha-1-anti-trypsin globules are seen in a disease called alpha-1-anti-trypsin deficiency, which affects both the liver and the lungs.
  • Zymogen granules: Zymogen granules are a specialized piece of cellular machinery that are normally found in salivary gland-type tissue. The tumour cells in a type of salivary gland cancer called acinic cell carcinoma will contain lots of zymogen granules and pathologists often perform this test to confirm the diagnosis.

This test is often performed at the same time as a periodic acid Schiff (PAS) stained slide. Unlike PAS-D, the PAS test does not include diastase. Pathologists perform these two tests together to look for glycogen inside a cell. These tests work well together because glycogen appears pink on the PAS-stained slide but clear on the PAS-D-stained slide.

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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