A method and apparatus for preventing and treating septicemia in patient blood is provided. The extracorporeal system includes an antimicrobial device to inactivate at least 99% of bloodborne microorganisms, a hemoconcentrator/filtration unit to remove approximately 50-75% of target molecules from the patient blood and a filter unit to remove target molecules from patient blood from the sieved plasma filtrate. Target molecules are produced by microorganisms, as well as by the patient's cells. These molecules include endotoxins from Gram negative bacteria, exotoxins from Gram negative and Gram positive bacteria, as well as RAP protein mediator from Staphylococcus aureus, and cell mediators such as tumor necrosis factor-alpha, and interleukin 1-beta, interleukin 6, complement proteins C3a and C5a, and bradykinin.