In 1945, Coombs, Mourant and Race described the use of anti-human globulin serum for detection of red cell-bound non-agglutinating antibodies and the antiglobulin (Coombs) test was rapidly applied. One cause of false negative antiglobulin tests is improper washing of the cells which results in free globulin molecules being present with supposedly washed cells and these globulins neutralise the antiglobulin serum when it is added. A negative result in an antiglobulin test should only occur when anti-human globulin is added to red cells that are not sensitised. To show that test cells were properly washed and that no neutralisation has occurred, antibody-coated cells are used as a positive indicator.