Therapeutic apheresis: treatment in search of a disease.

Blood has been recognized as the essence of life since ancient times. Bloodletting, however, was performed centuries ago to treat disease and prolong life. Seventy years ago selective removal of blood components from circulating blood was advocated as a therapeutic measure. However, manual procedures for blood removal, separation, and reinfusion were quite cumbersome and did not really lend themselves to daily clinical practice. In the last 15 years, technologies have been developed to allow separation of blood into its component fractions, selective removal of specific elements--either cellular products or liquid plasma--an reinfusion of the remaining blood. Early cell separators were designed to collect specific blood components from healthy donors for subsequent transfusion to critically ill patients. Apheresis techniques were found to reduce the amounts of some normal elements circulating in the donors' blood, and the procedure thus began to be used therapeutically to remove abnormal components and to reduce excessive quantities of otherwise normal blood components. Diffusion of automated cell separators quickly followed and apheresis procedures were applied as treatment for a variety of diseases and conditions. The efficacy of therapeutic apheresis in many rare or exotic diseases is well established. In others, the role of apheresis is less clear. By reviewing the medical benefits of therapeutic apheresis, access to treatment, and the costs resulting from broad applications, this assessment will assist health care professionals and policymakers to evaluate therapeutic apheresis technology.