In the Periodic Acid Schiff stain, there is no positive staining and the control is negative. Which action is recommended?

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In PAS staining, carbohydrates are revealed when periodic acid oxidizes them to aldehydes, which Schiff’s reagent then colors magenta. If you see no positive staining and the control is negative, the issue is with the reagents or procedure, not the tissue. The recommended action is to use fresh, properly stored reagents and run the stain again, ensuring every component is fresh and in date. Fresh Schiff’s reagent and periodic acid are critical because they can lose potency or become inactive over time; reusing old Schiff’s reagent or skipping steps (like the periodic acid oxidation) would prevent the reaction from producing color. Ignoring reagent freshness will lead to the same failure. After refreshing reagents, re-run with a known control to confirm the stain works.