Which stain is used as a control slide to detect iron deposition in tissue?

• A. Grocott's Methenamine Silver
• B. Masson's Trichrome
• C. Perl's Prussian Blue
• D. Luxol Fast Blue

Answer: (C)

Staining for iron relies on a reaction that specifically binds ferric iron to form a blue pigment. Perl's Prussian Blue does this by reacting ferric iron, present in hemosiderin and ferritin, with potassium ferrocyanide to yield ferric ferrocyanide, which turns blue. This makes it the method of choice to visualize iron deposits in tissue and to confirm iron overload conditions. In practice, a known iron-containing tissue can serve as a positive control to verify the stain is working. The other stains target different tissue components: Grocott's Methenamine Silver stains fungi and certain basement membranes; Masson's Trichrome highlights collagen and differentiates muscle; Luxol Fast Blue stains myelin.