Flow and image cytometry for DNA analysis in bladder washings: improved concordance by using internal reference for flow

Using flow or image cytometry, we compared the DNA distribution of cells from bladder washings from 52 patients with bladder cancer. For image cytometry, urothelial nuclei (recognized visually) were analyzed for DNA content using polymorphonuclear nuclei as internal diploid reference. For flow cytometry, two methods can be used: either all cells can be analyzed, as commonly performed, or urothelial cells can be analyzed alone, after specific detection. In this flow cytometry study, cells were doubly stained for panurothelial antigens T16 and for DNA. All the cells were first analyzed using peripheral lymphocytes as an external reference; 79% of the results were similar with results obtained from image analysis. For discordant results, flow-cytometric data were reprocessed to identify immunologically stained urothelial cells; one additional case became concordant with image cytometry when only urothelial cells were analyzed, with lymphocytes as diploid reference; a better concordance (94%) was found when the nonurothelial cells of the samples served as a diploid reference instead of peripheral lymphocytes. This suggests that we achieved an improvement of the flow-cytometric evaluations for ploidy assessment, and we conclude that, on these conditions, flow or image analysis can be considered as equivalent methods for DNA content studies of tumors.