Formalin pigment formation is associated with preparation in which type of solution?

• A. Very hypotonic
• B. Isotonic
• C. Hypertonic
• D. Colloid suspension

Answer: (A)

Formalin pigment (acid formaldehyde hematin) arises when tissue fixed in formalin encounters conditions that cause hemoglobin or heme to be released and oxidized in the presence of formaldehyde. Very hypotonic solutions cause cells, including red blood cells, to swell and rupture, releasing hemoglobin. The released heme then reacts with formaldehyde under acidic or unfavorable conditions to form the dark acid hematin pigment that can deposit in the tissue. Using neutral buffered formalin and avoiding hypotonic steps reduces this pigment formation. Isotonic and hypertonic environments keep cells from lysing as readily, and colloid suspensions don’t promote the release of heme in the same way, so they are not associated with pigment formation.