Regarding EDTA in decalcification, which statement is true?

• A. It damages tissues.
• B. It works very quickly.
• C. It is a chelating agent that allows immunohistochemical and enzyme reactions after use.
• D. It is not suitable for oxidative enzyme stains.

Answer: (C)

EDTA works by chelating calcium ions, slowly removing mineral content without the harsh effects of strong acids. This gentle decalcification preserves tissue morphology and especially preserves antigen sites, which is why immunohistochemical staining and many enzyme reactions can be performed after decalcification. The trade-off is that EDTA-based decalcification is slow compared with acid methods, but that slowness is the reason it is preferred when downstream IHC or enzyme histochemistry is needed. It does not typically damage tissues when used properly, and it actually lends itself to maintaining enzyme activity better than strong acids. That’s why the statement describing EDTA as a chelating agent that enables immunohistochemical and enzyme reactions after use is the true one.