What is the correct order of steps in the Periodic Acid Schiff stain?

Study for the CAMLPR Histology Practice Test. Study with flashcards and multiple choice questions, each question has hints and explanations. Get ready for your exam!

The key idea is that PAS staining detects carbohydrates by first oxidizing them with periodic acid to form aldehyde groups, then Schiff’s reagent binds to those aldehydes to give a magenta color. If glycogen is being tested, a diastase digestion is done first to prove glycogen was present by removing it before oxidation. After the color develops, a water rinse stops the reaction, and a hematoxylin counterstain provides nuclear contrast.

So the best sequence is diastase (if glycogen is being examined) followed by periodic acid, then Schiff’s reagent, then a water wash, then hematoxylin. This ordering is correct because Schiff’s reaction requires aldehydes created by periodic acid, and the diastase step must occur before oxidation if glycogen needs to be demonstrated. Other sequences place Schiff before oxidation or misplace the diastase step, which would prevent proper staining.