Staining is a technique used in histopathology to facilitate the identification of abnormalities in cell count and structure under the microscope. A variety of stains are used in histology. Stains change the colour of cells and tissues significantly. The most commonly used histologic stain is the H&E stain, which is used to differentiate tissue structures. In general, both H&E stain and PAS stain are used for tissue samples of organs as well as for blood smears.
What is H&E Stain?
Haematoxylin and eosin stain or H&E stain is one of the main tissue stains used in histology. It is the most common stain used in medical diagnosis and often the gold standard of stains. H&E is the combination of two stains used in histology. They are haematoxylin and eosin. The haematoxylin stains cell nuclei and gives a purplish-blue colour, while the eosin stains the cytoplasm and extracellular matrix in pink colour. Apart from the organelles that stain using H&E stain, other structures take on different shades with a mixture of these specific colours. Therefore, pathologists easily differentiate between nuclear and cytoplasmic parts of a cell as well as the overall tissue structure.
The H&E stain is considered the main stain in histology because it can be carried out faster, is inexpensive, and stains tissues in a way that a considerable amount of the microscopic anatomy is observed. This enables the diagnosis of a wide range of histopathologic conditions. The results of an H&E do not depend on the chemicals that are used in the protocol. This staining procedure involves the application of haematoxylin combined with a metallic salt or dye fixative followed by a rinse in a weak acid solution in order to remove excess staining. After the application of haematoxylin, the tissue is counterstained using eosin. Haematoxylin is a basic, positively charged, or cationic stain. Eosin is an acidic, negatively charged, or anionic stain.
What is PAS Stain?
Periodic acid-Schiff stain or PAS stain is a staining method used to detect polysaccharides, including glycogen and muco-substances, such as glycoproteins, glycolipids, and mucins in tissues. The periodic acid reactions oxidize the vicinal diols in these sugars by breaking the bond between adjacent carbons involved in the glycosidic linkages in the rings of monosaccharide units in long polysaccharides. This creates a pair of aldehydes at the two free tips of the broken monosaccharide rings. The oxidation process is regulated sufficiently in order to stop the aldehydes from oxidizing further. The aldehydes then react with Schiff reagent to give a purple-magenta colour. A basic stain is usually used as the counterstain during the procedure.
PAS stain is used in the diagnosis of several medical conditions such as glycogen storage disease, adenocarcinomas, Paget disease of the breast, alveolar soft part sarcoma, Whipple’s disease, liver hepatocyte stains, Mycosis fungoides, Sezary syndrome, Ewing sarcoma, erythroleukemia, fungal infections, pulmonary interstitial glycogenosis, pulmonary alveolar proteinosis, and ceroid lipofuscinosis. When using PAS stain on tissues, it is recommended that 10% neutral buffered formalin or Bouin solution used as a fixative. When PAS stain is used for blood smears, the recommended fixative is methanol.
What are the Similarities Between H&E and PAS Stain?
- H&E stain and PAS stain are histologic stains.
- They are used in the detection of abnormalities or diseases.
- Both consist of unique staining reagents.
- Tissue samples and blood smears are used as specimens in both staining procedures.
- Samples of both techniques are observed through a microscope.
- Both staining protocols include a counter stain.
What is the Difference Between H&E and PAS Stain?
H&E stain consists of hematoxylin and eosin, while PAS stain consists of periodic acid and Schiff reagent. Thus, this is the key difference between H&E and PAS stain. Moreover, H&E stain gives a purplish-blue color by hematoxylin and pink color by eosin. PAS stain gives a purplish-magenta color. Another difference between H&E and PAS stain is their use. H&E stain is used in the identification of cell nuclei, cytoplasm, and extracellular matrix, while PAS stain is used in the identification of polysaccharides and muco-substances.
The below infographic presents the differences between H&E and PAS stain in tabular form for side-by-side comparison.
Summary – H&E vs PAS Stain
H&E stain and PAS stain are staining techniques used in histopathology to facilitate the identification of abnormalities and diseases. H&E stain consists of two histopathologic stains; hematoxylin and eosin. PAS stain consists of periodic acid and Schiff reagent. H&E stain is one of the main tissue stains used in histology. Hematoxylin stains cell nuclei and gives a purplish-blue color, while eosin stains the cytoplasm and extracellular matrix in pink color. PAS stain is used to detect polysaccharides and muco-substances. The periodic acid oxidizes sugars, and the Schiff reagent reacts with the resulting aldehydes to give a purplish-magenta color. So, this summarizes the difference between H&E and PAS stain.
1. “Periodic Acid-Schiff Stain.” An Overview | ScienceDirect Topics.
2. Rachel Baxter BSc, MSc. “Interpretation of Histological Sections: Stains Used in Histology.” Kenhub, Kenhub, 7 July 2022.