Which statement about formalin pigment is correct?

• A. Formalin pigment is preventable and can be removed with alcoholic picric acid or alkaline alcohol.
• B. Formalin pigment is not preventable and cannot be removed.
• C. Formalin pigment is removable only with iodide-based reagents.
• D. Formalin pigment is prevented by using acetic acid.

Answer: (A)

Formalin pigment is a discoloration known as acid formaldehyde hematin that can form in tissues fixed with formalin, especially under acidic conditions or prolonged exposure. The practical point is that this pigment is preventable in the fixative stage by using neutral-buffered formalin, which keeps the pH near neutral, reducing the chemical environment that leads to pigment formation.

If pigment does appear, it can be removed after processing by treating the slides with alcoholic picric acid or with an alkaline alcoholic solution. These treatments dissolve or disrupt the pigment without harming the tissue sections.

Why the other ideas don’t fit: iodide-based reagents are not the standard method for removing formalin pigment, and using acetic acid does not prevent pigment formation (and in fact can promote acidic conditions that favor it).