Tuesday, 14 June 2011
Periodic-Acid Schiff Diastase (PASD) Special Stain – Method and Tips
In my previous post I covered the Periodic Acid-Schiff reaction (PAS) special stain which is by far the most common stain performed in a routine histology laboratory. A variation on this technique call the Periodic Acid-Schiff Reaction with diastase digestion (PASD) is another commonly performed special stain which I will be covering in this post.
The variation on the PAS technique involves simply exposing the section to the diastase enzyme amylase prior to continuing with the standard PAS method. The term ‘diastase’ refers to any enzyme that catalyses the breakdown of starch into maltose the dextrose. The diastase enzyme acts by cleaving the a-glucosidic 1-4 linkages of starch or glycogen (aka animal starch) leading to the formation of maltose and dextrose (maltose and dextrose are water-soluble sugars). So when sections are pre-exposed to diastase before commencing the PAS technique the glycogen within the tissue is broken down into maltose and dextrose which are dissolved and washed away when the section is rinsed sufficiently in tap water.
The diagnostic purpose of performing the PASD technique include
- the removal of glycogen to make it easier to identify mucins stained by the PAS technique
- analysis of glycogen deposits within the liver
- highlighting a thickened basement membrane for example in lupus
Diastase solution – 1 part human saliva to 9 parts distilled water.
1% aqueous periodic acid – from PAS method.
Schiffs Reagent – from PAS method.
1. Take sections to water.
2. Expose sections to diastase solution for 30 minutes at room temperature.
3. Wash sections thoroughly in tap water.
3. Continue with PAS method from step 2.
- Always run a PAS and a PASD control with every batch of PASD stains to ensure your diastase solution is working. This author has found a glycogen rich liver control to be most sufficient. This author also runs a PAS and PASD for all PASD requests.
- Commercial amylase is available instead of using a saliva solution. Commerical amylase sometimes requires different incubation temperatures and conditions so check this before using. This author has found that a saliva solution is easiest due to its ease of preparation, availability and plus it is free.
- Put all sections onto to ‘sticky’ slides ie. Superfrost plus slides or their equivalent as the saliva solution causing some lifting of the section from the slide. This is reportedly more prevalent in sections exposed to the commercial amylase solution.
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