Which stain uses paraldehyde in the primary stain?

• A. Aldehyde fuchsin
• B. Van Gieson
• C. Masson trichrome
• D. Oil Red O

Answer: (A)

Aldehyde fuchsin is the stain that uses paraldehyde in the primary stain. The aldehyde component from paraldehyde couples with the fuchsin dye to form a chromogen that specifically binds elastin, so elastic fibers appear deep magenta. This aldehyde-in-the-stain chemistry is what sets aldehyde fuchsin apart from the others. The other stains operate by different dye chemistries: Van Gieson uses picric acid and acid fuchsin to differentiate collagen and muscle; Masson trichrome uses a trio of dyes (blue, red, green) to distinguish connective tissue components; Oil Red O stains lipids in frozen sections without employing aldehyde in the staining step.