B2M and malnutrition: PMMA filters are able to remove middle and large molecules such as cytokines (like IL-6); middle molecules, such as beta 2 microglobulin (B2M), removed by convective therapy, maintaining the diffusive clearance of small molecules like urea with a great biocompatibility [123]; and a lower sieving coefficient for albumin in order to avoid catabolism and malnutrition [124].