Which tissues are used as controls for neutral mucins staining with PAS?

• A. Kidney and stomach
• B. Liver and pancreas
• C. Brain and spinal cord
• D. Skin and muscle

Answer: (A)

Neutral mucins give a magenta color with PAS, so you need tissues that reliably contain neutral mucins to confirm the staining worked. The stomach’s surface mucous cells produce neutral mucins, so their mucous layer stains strongly with PAS and serves as a clear positive control. The kidney also contains neutral mucin–like glycoproteins in its tubular secretions, providing another dependable site of PAS positivity. Together, they validate that the stain is detecting neutral mucins rather than other components.

Other tissues—liver and pancreas, brain and spinal cord, or skin and muscle—don’t consistently provide robust neutral mucin content for a reliable positive control. They may lack significant neutral mucins or produce mainly other substances (glycogen, neural components, or structural proteins) that wouldn’t demonstrate the same clear PAS-positive reaction as neutral mucins do.