AbstractBackgroundThe use of cell block (CB) preparation is underused in urine cytology (UC) and varies among hospitals. In addition to confirming a diagnosis, CBs can be useful in cases of metastatic disease, diagnoses requiring immunohistochemical (IHC) staining, and for ancillary studies. The role of this study is to examine the performance of CBs for UC at three affiliated teaching hospitals.Materials and MethodsA retrospective review of UC cases with a CB was conducted at a county hospital, Veterans Affairs hospital, and tertiary university‐based hospital. For each specimen, patient demographics, specimen type, volume, original diagnosis, and IHC stains were recorded. Each case was reviewed for diagnosis based on ThinPrep alone, diagnosis based on ThinPrep and CB, utility of CB for diagnosis, and CB cellularity.ResultsA total of 250 UC specimens with CB from 186 patients was identified. Bladder washes were the most common (72.1%). IHC stains were performed on 17.2% of cases. On blinded review, CB preparation was deemed useful in 61.2% of cases, with the highest rate for suspicious for high‐grade urothelial carcinoma (SHGUC) cases (87.0%). The diagnosis based on ThinPrep review changed with incorporation of CB in 13.2% of cases, with the highest rate for SHGUC cases (43.5%).ConclusionsThe results demonstrate that use of CB in UC confirms the final diagnosis in more than one‐half of cases and changes the diagnosis in a subset of cases. Use of CB was most helpful in the SHGUC category. Further evaluation of the types of cases in which CB are prepared is warranted.