Formalin fixation stabilizes lipids.

• A. True
• B. False
• C. Only at high temperatures
• D. Only when used with acetic acid

Answer: (B)

Lipids are not stabilized by formalin. Formalin fixes tissue mainly by crosslinking proteins, forming a network that preserves cellular architecture. Lipids don’t participate in this crosslinking and are prone to being dissolved or removed during the dehydration and clearing steps used to process tissue for embedding. Because of that, lipid preservation isn’t achieved with formalin fixation alone. If lipids need to be preserved or visualized, alternative methods such as osmium tetroxide postfixation, freeze-substitution, or using fresh-frozen sections are employed. The idea that formalin stabilizes lipids is not correct, and changing temperature or adding acetic acid does not make formalin lipid-stabilizing.