Diagnostic cytology in veterinary medicine: a comparative and evidence-based approach.

Diagnostic cytology is a core veterinary pathology service involving specimens from domestic animals, laboratory animals, and exotic species. Evidence-based application of cytopathology involves management of preanalytical factors, and thorough evaluation of the diagnostic accuracy of the technique in each species and for all specimen types. Unique to veterinary medicine is the reliance on cytology as the basis for crucial medical decisions such as humane euthanasia, especially when the patient is critically ill or when financial considerations limit diagnostic and therapeutic options. This article reviews the cytologic criteria for the diagnosis of selected neoplastic and infectious diseases.