In the process of tissue sectioning, when some tissues contain bone or calcification foci, the calcium-containing tissues should not be directly embedded with paraffin. This is because the density between calcium and paraffin is different, and it is more difficult to cut a complete section. It is best to fix the calcium-containing tissue before decalcification or both. Downstream operations such as dehydration, transparency, waxing, embedding, and slicing are then performed. There are many reagents used for decalcification, including organic acids, inorganic acids, ethylenediamine tetraacetic acid (EDTA) and electrolytic decalcification. EDTA is a relatively good chelating decalcification agent, which has minimal effect on tissue structure and can preserve some enzymes of tissues well. The tissues decalcified by EDTA can be stained by immunohistochemistry and in situ hybridization. However, the decalcification rate is too slow, generally taking weeks to months.

Formalin-edta decalcification solution (enzyme protection type) is mainly composed of formalin-EDTA, enzyme protectants, etc., with a pH value of about 7.2-7.4, which can combine tissue fixation and decalcification. Its advantages are: (1) The tissue staining results of decalcification by EDTA are good; (2) The structural damage to the tissue is smaller than that of conventional EDTA decalcified solution; ③ Reduce the loss of ALP enzyme activity in decalcified bone.