No staining of the glomerular basement membrane can be seen microscopically on a control section of kidney. This may be the result of

• A. Inadequate oxidation
• B. Overoxidation
• C. Poor embedding
• D. Dehydration

Answer: (A)

In PAS staining, oxidation with periodic acid is needed to convert carbohydrate components of the basement membrane into aldehyde groups that react with Schiff reagent to produce the magenta color. If this oxidation step is inadequate, there aren’t enough aldehyde groups to react, so the glomerular basement membrane fails to stain, even in a control kidney section. That’s why inadequate oxidation is the most plausible reason for no staining observed.

Overoxidation can also reduce staining by destroying aldehyde groups, but the typical, most likely cause when a control section shows no staining is insufficient oxidation. Poor embedding or dehydration would cause broader tissue artifacts or poor morphology rather than a specific loss of basement membrane staining.