PASpositiven

PASpositiven, often referred to as PAS-positive, denotes cells, tissues, or substances that react with the Periodic acid–Schiff (PAS) stain in histology and pathology. The PAS reaction highlights carbohydrates, including glycogen, glycoproteins, glycolipids, mucopolysaccharides, and basement membranes, producing a magenta color in areas rich in these substances.

The staining mechanism involves oxidation of vicinal diols in carbohydrates by periodic acid to generate aldehyde groups, which then react with the Schiff reagent to yield the characteristic color. To distinguish glycogen from other PAS-positive substances, diastase digestion can be applied before PAS staining; glycogen is digested away and the reaction becomes diastase-PAS negative.

PASpositiven has broad diagnostic utility. It aids in identifying fungal infections in tissue sections, since many fungal cell walls contain polysaccharides that stain with PAS (for example, Candida species). It also highlights mucins and other secreted glycoproteins in glandular tumors, supporting tumor characterization. In renal pathology, PAS staining outlines basement membranes and mesangial matrix, helping assess glomerular disease; thickening or disruption of the basement membrane can be visualized, contributing to evaluations in conditions such as diabetic nephropathy or membranous nephropathy. Additional applications include detection of glycogen storage in liver and muscle and assessment of various mucopolysaccharide-rich structures.

Limitations include a lack of specificity: many carbohydrate-rich substances stain PAS-positive, so interpretation must rely on morphological context and appropriate controls. Positive findings should be correlated with clinical information and, when needed, complemented by other stains or immunohistochemical markers.