Which stain highlights basement membranes in kidney and other tissues?

• A. Hematoxylin and eosin (H&E)
• B. Masson's trichrome
• C. Giemsa
• D. Periodic acid–Schiff (PAS) stain.

Answer: (D)

Stains that target carbohydrate-rich structures reveal basement membranes. The periodic acid–Schiff stain uses periodic acid to oxidize sugars in glycoproteins and proteoglycans to form aldehydes, which then react with Schiff reagent to produce a magenta color. In the kidney, the glomerular basement membrane and the surrounding mesangial matrix are rich in these carbohydrates, so they stain vividly with PAS, making it especially useful for assessing basement membrane thickness and pathology in glomerular disease. Other stains serve different purposes: routine H&E highlights general tissue architecture but not basement membranes specifically; Masson's trichrome emphasizes collagen; Giemsa stains cells and certain microorganisms.