Abstract
EDTA anticoagulated plasma is the preferred testing specimen for the majority of blood bank testing today. EDTA in specimen collection tubes prevents the in vitro fixation of complement by chelating calcium. Antibodies in several blood group systems, such as Kidd, Kell, and Lewis, can bind complement and rarely may only be detectable when complement is present. Adding fresh ABO-compatible serum as a source of complement when one of these antibodies is suspected is a means to enhance their reactivity and identify and confirm their specificity.