**4. Which factors determine endotoxin concentration in dialysis fluid?**

The current requirements of dialysis fluid are set out in the ANSI/AAMI/ISO 23500 standards series on the preparation and quality management of fluids for hemodialysis and related therapies. There are two potential sources of endotoxins, water and concentrates, and there is the option to use ultrafilters for endotoxin removal. The water system provides water to the monitor in accordance with the provisions of ANSI/ AAMI/ISO 23500-3 (formerly ISO 13959) [8], which defines maximum endotoxin concentration as 0.25 EU/ml for water for dialysis. Concentrates to prepare dialysis fluid to follow the provisions of ANSI/AAMI/ISO 23500-4 (formerly ISO 13958) [9]. Endotoxin concentrations in concentrates must be at a level that allows the preparation of standard dialysis fluid with a maximum of 0.5 EU/ml from concentrate and water for dialysis. The maximum endotoxin concentration for standard dialysis fluid is governed by ANSI/AAMI/ISO 23500-5 (formerly ISO 11663) [10]. If an ultrafilter is used to filtrate the prepared dialysis fluid, ultrapure dialysis fluid can be prepared with a maximum allowed endotoxin concentration of 0.03 EU/ml.

In this work, the assumption is made that dialysis fluid of at least standard dialysis fluid quality per ANSI/AAMI/ISO 23500-5 [10] is provided by the dialysis monitor, and maximum endotoxin concentration is at 0.5 EU/ml even if no ultrafilter is used or in case of failure of the ultrafilter.
