Comparison of flow cytometry and heterotrophic plate count methods for dialysis water microbial monitoring

Water is an essential component of renal replacement therapy by dialysis. Haemodialysis patients undergoing 4-hour dialysis sessions, thrice weekly, may be exposed to more than 360 L of dialysis fluid per week. Dialysis water and ultrapure dialysis fluids have been established as a prerequisite for online convective therapies (namely haemodiafiltration), to improve biocompatibility of the dialysis system and to reduce inflammation profile of the dialysis patients. The microbial quality of dialysis water should be monitored regularly to demonstrate the effectiveness of the disinfection protocol. Current water and dialysis fluids microbial quality assessment is typically done via heterotrophic plate counts (HPC) and endotoxins analysis. Plate counts methodology provides information on the microbial content of the water only after a considerable incubation time (typically 7 days). Flow cytometry (FCM), as a rapid alternative method, provides the possibility of real-time corrective actions and greater patient safety. In this study, we compared the outcomes of dialysis water microbial quality in an existing dialysis clinic, using two different measurement methods, HPC and FCM, to test the possible benefits of applying FCM as a valid alternative method for dialysis water microbial monitoring. We conclude that FCM offers higher sensitivity than HPC for microbial monitoring of dialysis water, potentially enabling earlier corrective actions. More extensive and larger studies are needed, namely, to evaluate the possible added value of FCM method in dialysis fluids monitoring. If the FCM method is confirmed, it will be necessary to establish maximum allowable levels and typical action levels for dialysis water and dialysis fluids quality when using FCM.