In Prussian Blue staining, what color does ferric iron (hemosiderin) appear?

• A. Blue
• B. Red
• C. Green
• D. Yellow

Answer: (A)

Prussian Blue staining detects ferric iron (Fe3+) by forming a blue pigment. The ferric iron in hemosiderin reacts with potassium ferrocyanide to create ferric ferrocyanide, an insoluble blue compound known as Prussian blue. Because this reaction specifically produces blue, iron deposits in tissue sections appear blue under the microscope. The other colors don’t result from this chemical reaction, which is why blue is the characteristic appearance for ferric iron in Prussian Blue stains.