New insights into the management of anemia in the surgical patient.

Although the safety of allogeneic blood transfusion has increased dramatically in recent decades, some risks remain. Contamination with infectious agents-including viruses, bacteria, spirochetes, and parasites-is still possible, although recent advances in blood screening and testing have decreased the risk. The principal noninfectious complication of blood transfusion is immunomodulation. Clinical manifestations of transfusion-related immunomodulatory activity include hemolytic and allergic reactions, graft-versus-host disease, the possible decreased survival in patients with cancer, as well as increased susceptibility to postoperative infection, activation of latent infection, improvement in organ allograft survival, decreased frequency of spontaneous abortion, and moderation of immune inflammatory disease. The cause of transfusion-related immunosuppression is not yet known, but possible contributing factors are the development of a suppressor cell network, formation of anti-idiotype antibodies, clonal deletion, macrophage paralysis, up-regulation of cells with latent infections, cytokine infusion, and contamination by infectious and noninfectious agents.