Black-brown deposit on bloody tissue birefringent under polarized light is due to which fixative and pigment, and how is it prevented?

Study for the CAMLPR Histology Practice Test. Study with flashcards and multiple choice questions, each question has hints and explanations. Get ready for your exam!

Acid hematin pigment is the clue here. It forms when tissue, especially blood-rich areas, is fixed in an acidic (unbuffered) formalin fixative. The formalin or the acidic environment converts heme into hematin, giving a black-brown deposit that is birefringent under polarized light. That specific combination—unbuffered formalin producing acid hematin pigment in bloody tissue—fits the description.

To prevent this, use a buffered (neutral) formalin fixative, which avoids the acidic conditions that drive hematin formation. If you still need to prevent it in specimens fixed with potentially acidic reagents, using alcoholic picric acid or alkaline alcohol with acetic acid can help neutralize conditions and stop pigment formation. The other fixatives produce different pigments (for example, chromate pigment with dichromate fixatives, osmium pigment with osmium fixatives, or picrate pigment with picric acid fixatives) and do not match this scenario.