Neutral lipids stained with Oil Red O in a wax-embedded block show which result?

• A. Not demonstrated
• B. Red to orange
• C. Blue
• D. Grey

Answer: (A)

Oil Red O stains neutral lipids red, but it only works on preserved lipids in frozen tissue. In wax-embedded (paraffin) sections, the lipid is extracted during dehydration and clearing, so there’s nothing for Oil Red O to bind. That’s why neutral lipids are not demonstrated in a wax-embedded block stained with Oil Red O. If the tissue were prepared as a frozen section, you would expect a red-orange lipid staining pattern.