Cytology is the microscopic examination of cell samples. These samples can be collected from any area of the body. Cytology is often used to diagnose growths or masses (tumors) found on the surface of the body, but can also be used to assess bodily fluids, internal organs (e.g., liver, lung, lymph nodes, kidney), and abnormal fluids that may accumulate, especially in the chest and abdomen.

Histopathology is the examination of samples of whole tissues and is performed on a solid piece of tissue that has been collected surgically.

The piece of tissue is prepared through a process called histology by preserving, thinly slicing or sectioning, and staining the tissue sample with dyes. Once prepared, the tissue sections are examined under the microscope by a veterinary pathologist. Histopathology focuses on the architecture of the tissue and provides more information about the tissue than cytology.