The present invention concerns a multipart fluid system for use in CRRT,wherein the multipart fluid system comprisesan anticoagulation fluid and at least one fluid from the group consisting of adialysis fluid and an infusion fluid. Accordingto the invention the anticoagulation fluid comprises at least 8 mM citrate,and the dialysis fluid and/or infusion fluid comprises2-8 mM citrate and 1-5 mM total calcium. The present invention furtherconcerns a system for regional citrate anticoagulation inan extracorporeal blood circuit.