Acronym for “Low Ionic Strength Saline.” LISS is used in blood bank testing to potentiate reactions between antibodies and red blood cells. Under normal testing conditions, red blood cells have a negative surface charge, and sodium ions (Na⁺) in saline solutions aggregate around the red cell surface. This creates a net positive electrical charge, and the similar charge on all RBCs causes them to repel each other (this is also known as “zeta potential”). Since LISS contains fewer sodium ions than “normal” saline, fewer Na⁺ ions are available to congregate at the RBC surface, and thus, the zeta potential is lessened, allowing antibodies to work more efficiently to agglutinate incompatible red cells.