Which preparation yields red to orange color for Oil Red O staining of neutral lipids?

• A. Cryostat cut
• B. Wax block cut
• C. Paraffin section
• D. Frozen section

Answer: (A)

Oil Red O specifically stains neutral lipids, so the lipids must be preserved in the tissue for the dye to bind and show color. Routine paraffin processing uses solvents like xylene and alcohol that extract and remove lipids, so paraffin-embedded sections won’t reveal the lipid content with Oil Red O. The only prep that preserves lipids for this stain is a frozen section, cut in a cryostat. That keeps the lipids intact and allows Oil Red O to color them red to orange. A cryostat cut is a frozen section, so it yields the expected staining. Wax block cuts and paraffin sections lose lipids during processing and won’t show the lipid staining.