Formalin pigment can be removed from tissue by which solution?

• A. Alcoholic picric acid
• B. Iodine
• C. Alcohol
• D. Sodium hydroxide

Answer: (A)

Formalin pigment, also known as acid hematin, forms in tissues fixed with formalin and can obscure nuclear detail. The best way to remove it is by using alcoholic picric acid because the picrate complex formed in alcohol dissolves acid hematin, bleaching or dissolving the pigment without overly affecting the hematoxylin staining. Alcohol alone isn’t as effective at removing the pigment, iodine doesn’t target this pigment, and sodium hydroxide can bleach or damage tissues rather than selectively removing the pigment. So, alcoholic picric acid is the appropriate choice because it specifically dissolves formalin pigment while preserving the rest of the stain.