What should not be reported as atypia in urine cytology

The term “atypia,” although not well characterized, is widely used in diagnostic surgical and cytopathology. Because there are no guidelines regarding when to use this term, in the majority of cases, it is used as a “wastebasket.” This definitely applies to urine cytology, where the reported rate of atypia ranges from 1.9% to 23%. This review lists a number of cytomorphologic findings in urine cytology that are associated with known and specific causes. Urine specimens in which the morphologic changes can be attributed to particular etiologic factors should no longer be classified as “atypical.” These include urine specimens showing reactive umbrella cells or seminal vesicle cells, reactive changes due to stones, cytologic changes characteristic of infectious processes or therapy effect, instrumented urines with pseudopapillary clusters, and urinary diversion specimens.