**8. What should a requirement for the endotoxin barrier property of a dialyzer membrane look like?**

The calculations above show different endotoxin retention requirements for standard dialysis fluid and ultrapure dialysis fluid. Although the use of ultrapure dialysis fluid is recommended and it is not mandatory, and in the case of the absence or failure of an ultrafilter, only standard fluid quality can be assumed. Consequently, a requirement must orient itself to the use of standard dialysis fluid quality.

For standard dialysis fluid, a dialyzer membrane must have a minimum endotoxin retention capacity measured as an LRV of 2 after exposure to blood plasma and the formation of a protein layer, and it must have a minimum LRV of 1 in its protein-free pristine form.

Is this a realistic requirement for current, state-of-the-art dialyzer membranes? The LRVs of dialyzer membranes with a protein layer are well documented under treatment conditions. Polyflux L (low flux), Revaclear (high flux), and Theranova (medium cut-off) dialyzers were tested in various experimental configurations using mixed filtrates of *Pseudomonas aeruginosa* and *Pelomononas saccharophila* [17], lysates of *Pseudomonas aeruginosa* and isolated LPS from *Escherichia coli* [18]. In all cases, the LRV was above 2 [18]. Experimental data in the perspective of this

work is not available for pristine membranes. An experimental study is described in the sections below to provide data to answer the question if the minimum LRV requirement of LRV 1 is realistic for state-of-the-art dialyzer membranes before protein contact.
