Formalin pigment AFH is caused by which condition in tissue processing?

• A. Acidic pH and presence of blood
• B. Alkaline pH
• C. Low temperature
• D. High oxygen levels

Answer: (A)

Formalin pigment AFH happens when tissue that contains blood is fixed in formalin that is acidic. In that acidic environment, the heme from blood is converted to hematin, and this hematin reacts with formalin to form an insoluble brown-black pigment inside the tissue. That’s why the presence of blood and a low, acidic pH are the key conditions that produce this pigment.

Alkaline pH wouldn’t promote this pigment formation, and lowering the temperature or altering oxygen levels doesn’t drive the reaction in the way acidic formalin does. To prevent AFH, use neutral-buffered formalin (pH near 7) and fresh fixative, ensuring appropriate fixation and washing.