Periodic acid–Schiff–diastase (PAS-D, PAS diastase) stain is a periodic acid–Schiff (PAS) stain used in combination with

diastase A diastase (; from Greek διάστασις, "separation") is any one of a group of enzymes that catalyses the breakdown of starch into maltose. For example, the diastase α-amylase degrades starch to a mixture of the disaccharide maltose; the ...

, an enzyme that breaks down

glycogen Glycogen is a multibranched polysaccharide of glucose that serves as a form of energy storage in animals, fungi, and bacteria. It is the main storage form of glucose in the human body. Glycogen functions as one of three regularly used forms ...

. PAS-D is a

stain A stain is a discoloration that can be clearly distinguished from the surface, material, or medium it is found upon. They are caused by the chemical or physical interaction of two dissimilar materials. Accidental staining may make materials app ...

often used by pathologists as an ancillary study in making a histologic diagnosis on paraffin-embedded tissue specimens. PAS stain typically gives a

magenta Magenta () is a purple-red color. On color wheels of the RGB color model, RGB (additive) and subtractive color, CMY (subtractive) color models, it is located precisely midway between blue and red. It is one of the four colors of ink used in colo ...

color in the presence of glycogen. When PAS and diastase are used together, a light pink color replaces the deep magenta. Differences in the intensities of the two stains (PAS and PAS-D) can be attributed to different glycogen concentrations and can be used to semiquantify glycogen in samples. In practice, the tissue is deparaffinized, the diastase incubates, and the PAS stain is applied. An example of PAS-D in use is in showing gastric/ duodenal

metaplasia Metaplasia () is the transformation of a cell type to another cell type. The change from one type of cell to another may be part of a normal maturation process, or caused by some sort of abnormal stimulus. In simplistic terms, it is as if the ...

in duodenal

adenoma An adenoma is a benign tumor of epithelium, epithelial tissue with glandular origin, glandular characteristics, or both. Adenomas can grow from many glandular organ (anatomy), organs, including the adrenal glands, pituitary gland, thyroid, prosta ...

s. PAS diastase stain is also used to identify alpha-1 antitrypsin globules in hepatocytes, which is a characteristic finding of

alpha-1 antitrypsin deficiency Alpha-1 antitrypsin deficiency (A1AD or AATD) is a genetic disorder that may result in lung disease or liver disease. Onset of lung problems is typically between 20 and 50 years of age. This may result in shortness of breath, wheezing, or an inc ...

. PAS diastase stain is also used in diagnosing Whipple’s disease, as the foamy

macrophages Macrophages (; abbreviated MPhi, φ, MΦ or MP) are a type of white blood cell of the innate immune system that engulf and digest pathogens, such as cancer cells, microbes, cellular debris and foreign substances, which do not have proteins that ...

that infiltrate the

lamina propria The lamina propria is a thin layer of connective tissue that forms part of the moist linings known as mucous membranes or mucosae, which line various tubes in the body, such as the respiratory tract, the gastrointestinal tract, and the urogenital ...

of the small intestine in this disease possess PAS-positive, diastase-resistant inclusions.

Additional images

Image:Histoplasma pas-d small.jpg, Histoplasma. PAS diastase stain. Image:Histoplasma in granuloma pas-d.jpg, Histoplasma in a

granuloma A granuloma is an aggregation of macrophages (along with other cells) that forms in response to chronic inflammation. This occurs when the immune system attempts to isolate foreign substances that it is otherwise unable to eliminate. Such sub ...

. PAS diastase stain.

References

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External links

PAS Diastase Protocol
Staining

Additional images

See also

References

External links