What is the fixative for Oil Red O?

• A. 10% NBF
• B. Bouin
• C. Osmium tetroxide
• D. Zenkers

Answer: (A)

Oil Red O targets neutral lipids, so preserving lipid content in the tissue during preparation is essential. An aqueous fixative that crosslinks proteins without dissolving lipids provides the best balance for staining lipids in frozen sections. Ten percent neutral buffered formalin fits this role well: it stabilizes tissue architecture while keeping lipids in place for subsequent Oil Red O staining.

In contrast, fixatives containing organic solvents or aggressive lipid-modifying components can extract or alter lipids, leading to poor or inconsistent staining. Bouin solution has picric acid and ethanol, which can affect lipid preservation. Osmium tetroxide fixes lipids strongly but changes the tissue in ways that aren’t compatible with standard Oil Red O protocols. Zenkers fixative includes acetic acid, which can promote lipid loss or distortion.

So, the fixative that best preserves lipids for Oil Red O staining is 10% neutral buffered formalin.