In liver failure, hydrophobic toxins accumulate in the blood circulation. To support hepatic function, extracorporeal blood purification systems have been developed, in which both cationic and neutral adsorbents are used to remove albumin-bound metabolites from blood. An issue of these systems is the additional of coagulation factors containing negatively charged gamma-carboxyglutamate (Gla) domains, which, in physiological conditions, are shielded by calcium ions. We hypothesized that complexation of calcium ions by citrate leads to exposure of negative Gla domains, resulting in their binding to the positively charged adsorbents. The data presented here confirm that the binding of coagulation factors containing Gla domains to positively charged-polymers is enhanced in the presence of citrate as compared to heparin. This effect increased with increasing charge density of the polymer and has important implications for the clinical application of positively charged polymers.