The preferred fixative for the Warthin-Starry stain is which solution?

• A. 10% NBF
• B. 70% ethanol
• C. Acetone
• D. Bouin's solution

Answer: (A)

The key idea is that Warthin-Starry silver staining is highly fixation-sensitive and needs a fixative that preserves tissue without introducing substances that interfere with the silver reaction. 10% neutral buffered formalin fits this requirement well: it preserves morphology, maintains the chemical environment necessary for silver deposition on the targeted organisms, and does not leave residues that can cause excessive background or block the staining reaction.

In contrast, Bouin’s solution contains picric acid and can produce strong background staining and chemical changes that hamper the silver reduction step, while organic solvents like 70% ethanol or acetone can over-dehydrate or over-fix tissues, leading to poor penetration and inconsistent staining.