Which histochemical stain is used to demonstrate ferric iron in tissue sections?

• A. Perl's Prussian Blue
• B. Schiff's reagent
• C. PAS
• D. Congo Red

Answer: (A)

To see ferric iron in tissue, you need a reaction that turns iron deposits into a visible pigment. The Perls' Prussian Blue method uses acid to liberate ferric iron from storage forms, then potassium ferrocyanide reacts with the ferric iron to form insoluble ferric ferrocyanide, known as Prussian blue. This produces distinct blue granules wherever iron is concentrated (such as hemosiderin in macrophages or ferritin-rich areas), making iron stores clearly detectable under light microscopy. Other stains mentioned target different substances—Schiff's reagent and PAS highlight carbohydrates and related aldehydes, while Congo Red stains amyloid—so they do not visualize iron.