Accuracy of grading of urothelial carcinoma on urine cytology: an analysis of interobserver and intraobserver agreement.

BACKGROUND Urine samples of known urothelial carcinoma were independently graded by 3 pathologists with (MS, MR) and without (AO) fellowship training in cytopathology using a modified version of the 2004 2-tiered World Health Organization classification system. By measuring interobserver and intraobserver agreement among pathologists, compared with the gold standard of biopsy/resection, specimen accuracy and reproducibility of grading in urine was determined. METHODS 44 urine cytology samples were graded as low or high-grade by 3 pathologists with a 2-3 week interval between grading. Pathologists were blinded to their and others' grades and histologic diagnoses. Coefficient kappa was used to measure interobserver and intraobserver agreement among pathologists. Accuracy was measured by percentage agreement with the biopsy/resection separately for each pathologist, and for all pathologists and occasions combined. RESULTS The overall accuracy was 77% (95% C.I., 72%-82%). Pathologist AO was significantly more accurate than MR on occasion 1 (p = 0.006) and 2 (p = 0.039). No other significant differences were found among the observers. Interobserver agreement using coefficient kappa was unacceptably low, with all but one of the kappa value being less than 0.40, the cutoff for a "fair" degree of agreement. Intraobserver agreement, as measured by coefficient kappa, was adequate. CONCLUSIONS Our study underscores the lack of precision and subjective nature of grading urothelial carcinoma on urine samples. There was poor inter- and intraobserver agreement among pathologists despite fellowship training in cytopathology. Clinicians and cytopathologists should be mindful of this pitfall and avoid grading urothelial carcinoma on urine samples, especially since grading may impact patient management.