EDTA decalcifying solution (pH 7.2)

When tissues contain bone or calcified lesions, calcium-containing tissues are not suitable for direct paraffin embedding and sectioning. This is due to the difference in density between calcium and paraffin, which makes it difficult to obtain complete sections. For calcium-containing tissues, it is best to fix the tissue first, then decalcify, or perform both simultaneously. Subsequent steps include dehydration, clearing, paraffin infiltration, embedding, and sectioning. Various reagents are available for decalcification, including organic acids, inorganic acids, ethylenediaminetetraacetic acid (EDTA), and electrolytic decalcification.

EDTA is a relatively good chelating decalcifying agent that causes minimal damage to tissue structure and preserves certain enzymes in the tissue. Tissues decalcified with EDTA can be used for immunohistochemistry and in situ hybridization staining. However, this method is very slow, typically taking several weeks to months.