What is a Cell Block?

A cell block is a method of preparing cytologic material so that it can be processed, sectioned, stained, and viewed as a histology section. It can provide diagnostic information in addition to that obtained from cytology slides. It is easier to do special stains, and immunohistochemistry if needed, on a cell block rather than on cytology slides because the slides often require adaptations of the staining protocols and different controls.

It should be understood that the term 'block' in this context is not a reference to placing the cells in a paraffin block, but rather it refers to the technique of 'blocking' something to hold it together and maintain its shape. Remember when your grandmother was finished knitting or crocheting a sweater or doily and she would block it with starch to stiffen it and make it hold its shape?

A cell block is prepared using the material remaining after the cytology slides/smears have been made. The quality or quantity of those slides should never be sacrificed in order to make a cell block.