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Carbohydrate Stains
BCIT Histo Notes
| Question | Answer |
|---|---|
| Define Vicinal Diols or Glycols | OH group on adjacent carbons (in the vicinity), important atomic arrangement necessary for PAS staining |
| What accounts for Alcian Blue staining? | Presence of carboxylic acid groups (COOH) |
| Two most commonly requested special stains in pathology | PAS and Alcian Blue |
| What does the PAS stain identify? | glycogen and neutral glycoproteins |
| What does the Alcian Blue stain identify? | acid glycoproteins and proteoglycans |
| Important PAS positive substances | - glycogen - neutral glycoproteins - stomach - neutral glycoproteins - small bowel - basement membranes |
| The Two main steps of the PAS stain | 1. Oxidize carbohydrates (vicinal diols) w periodic acid to create aldehydes 2. Demonstrate the aldehydes w Schiffs reagent |
| What is the only cause of potential false positives with PAS stain? | certain lipids found in frozen sections and glutaraldehyde fixed sections |
| What is Schiff's reagent made of? | Basic Fuschin (mixture of dyes) or more commonly pararosaniline |
| What is added to Pararosaniline in order to make it colourless? | addition of sulphonic acid, sodium metabisulphite or thionyl chloride adds SO3 and destroys the chromophore, making the solution colourless |
| What occurs when the chromphore of Schiffs reagent binds aldehydes? | the chromophore is reestablished and it stains a magenta colour |
| Schiff's reagent is an example of a ______ dye | pseudoleuco dye |
| How can the effectiveness of Schiff's reagent be tested? | add 3 drops of the reagent to formalin/40% formaldehyde |
| How are we able to distinguish PAS staining due to glycogen from staining due to neutral glycoproteins? | diastase or amylase(saliva!) are specific enzymes for glycogen - if staining remains after treatment, then staining is due to neutral glycoproteins and not glycogen |
| Which infection can be detected by PAS? | Candida albicans - carbohydrates in the fungus can yield vicinal diols detected by PAS |
| Recall the pH and what mucins are ionized for Alcian Blue Staining | pH 2.5 - BOTH sulphated and carboxylated mucins are ionized pH 1.0 - ONLY sulphated mucins are ionized |
| In what order must PAS and Alcian Blue be performed on the same slide and why? | Alcian Blue FIRST, PAS second - Schiff's reagent introduces sulphonic acid groups that will stain positively w Alcian Blue - false positive |
| Which cancer can be characterized partially by being Alcian Blue Positive? | Mesothelioma - bad lung cancer |
| What is the cationic dye Alcian Blue used to detect? | Acid residues - sulphonic and carboxylic |
| Name the stain that can be used to demonstrate Cryptococcus neoformans | Southgate's Mucicarmine |
| Describe the colloidal iron method for demonstrating carbohydrates | Fe3+ (ferric) colloidal complex is electrostatically attracted to COOH and SO3H - ferric ions can then be demonstrated by potassium ferrocyanide *this is also the method for Perl's Prussian Blue |
| Name the typical control tissue for PAS stain | Liver - neutral mucins in portal triads and glycogen in hepatocytes |
| Name the typical control tissue for Alcian Blue | small or large intestine - there should be a variety of acid mucins in goblet cells other suitable tissues are umbilical cord and appendix |
Created by:
kenziebarroso