Counterstain option used along with aluminum hematoxylin in PAS includes which pigment?

• A. Eosin
• B. Light green
• C. Methylene blue
• D. Azure II

Answer: (B)

In PAS staining with aluminum hematoxylin, the goal is to get strong nuclear detail, vivid magenta for glycogen and other carbohydrates, and a contrasting background. Aluminum hematoxylin stains the nuclei blue-black, while the Schiff reagent products give a magenta color to polysaccharides and mucosubstances. To avoid clashing with that magenta and to keep nuclei distinct, a light, nonreactive counterstain is used for the background. Light Green provides a pale green background that contrasts nicely with both the magenta stain and the blue-black nuclei, giving clear differentiation of structures. Other counterstains like eosin would add pink tones that can muddy the magenta signal, and dyes such as methylene blue or Azure II would shift colors away from the desirable contrast obtained with light green.