Laboratory Techniques: Decalcification

Decalcification

A wide variety of calcified specimens are received in the surgical pathology laboratory. While some of these should be cut with specialized, expen-sive equipment, the vast majority of calcified specimens can be handled by a routine histology laboratory if they are appropriately decalcified. Decalcification is the process whereby calcium salts are removed from bone and other calcified tissues. Three general methods are employed to decalcify tissues. These include acid hydrolysis, organic chelation, and electrolysis (see Table 2-2). The important points to remember about decalcifying specimens follow:

1.  The tissue must be fixed before decalcification. In most cases, fixing a specimen for at least 24 hours in 10% neutral buffered formalin is adequate. If you use a different fixative, make sure that the fixative employed is compati-ble with the method of decalcification chosen.

2.  Decalcification should be carried out at room temperature and with constant magnetic stir-ring. While heat accelerates decalcification, it also induces numerous artifacts and thus should be avoided.

3.  Do not decalcify longer than necessary, as ex-cessive decalcification will introduce artifacts. To avoid overdecalcification, delicate tissues should be examined every hour and larger tissues examined as established by labora-tory protocol.

4.  Residual acid will destroy nuclear detail. Therefore, acid decalcification solutions must be removed from bone specimens before they are processed by washing them in water for at least 24 hours.

5.  The volume of the decalcification solution should be 10 to 15 times that of the tissue being decalcified. These solutions should also be changed on a regular basis.