Which treatment can remove the brown pigment from formalin-fixed tissue?

• A. Alcoholic Picric Acid
• B. Hydrogen Peroxide
• C. Sodium Chloride
• D. Acetic Acid

Answer: (A)

Formalin pigment, also called acid hematin, forms in formalin-fixed tissue when formaldehyde reacts with heme-containing compounds. This brown pigment can interfere with staining, so removing it is important. Alcoholic picric acid dissolves acid hematin, pulling the pigment out of the tissue sections and clearing the background for proper staining. Hydrogen peroxide can bleach some pigments but isn’t a reliable method for formalin pigment removal. Sodium chloride and acetic acid do not effectively remove acid hematin. So the treatment that best removes the brown pigment is alcoholic picric acid.