page_title: Staining
section_title: PAS staining
hierarchical_section_title: Staining / Specific techniques / PAS staining
caption_attribution_description: English: Micrograph showing Histoplasmosis. Liver biopsy. Periodic acid-Schiff diastase (PAS-D) stain. Histoplasma = clumps of small bright red circles. Related images PAS-D. PAS-D. PAS-D. GMS.
context_page_description: Staining is a technique used to enhance contrast in samples, generally at the microscopic level. Stains and dyes are frequently used in histology and in the medical fields of histopathology, hematology, and cytopathology that focus on the study and diagnoses disease at a microscopic level. Stains may be used to define biological tissues, cell populations, or organelles within individual cells.
  In biochemistry it involves adding a class-specific dye to a substrate to qualify or quantify the presence of a specific compound. Staining and fluorescent tagging can serve similar purposes. Biological staining is also used to mark cells in flow cytometry, and to flag proteins or nucleic acids in gel electrophoresis.
  Staining is not limited to biological materials, it can also be used to study the structure of other materials for example the lamellar structures of semi-crystalline polymers or the domain structures of block copolymers.
context_section_description: Periodic acid-Schiff is a histology special stain used to mark carbohydrates (glycogen, glycoprotein, proteoglycans). PAS is commonly used on liver tissue where glycogen deposits are made which is done in efforts to distinguish different types of glycogen storage diseases. PAS is important because it can detect glycogen granules found in tumors of the ovaries and pancreas of the endocrine system, as well as in the bladder and kidneys of the renal system. Basement membranes can also show up in a PAS stain and can be important when diagnosing renal disease. Due to the high volume of carbohydrates within the cell wall of hyphae and yeast forms of fungi, the Periodic acid -Schiff stain can help locate these species inside tissue samples of the human body.
caption: PAS diastase showing the fungus Histoplasma.
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