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.

In a negative antiglobulin test the anti-human globulin should remain active and this can be demonstrated by the addition of IgG sensitised cells. Agglutination of the IgG sensitised cells after mixing and centrifuging confirms that the anti-human globulin was added to the test, that the test cells were properly washed and all free globulin molecules were removed and that the anti-human globulin was active. Failure of the IgG sensitised cells to agglutinate indicates that the original negative antiglobulin test result is not valid and testing must be repeated.

Lorne Coombs Control Cells are made up of a 2-3% suspension of single donor group O red cells washed to remove all blood group antibodies and then resuspended in a preservative solution. The preservative solution contains neomycin sulphate (0.1 mg/ml) and chloramphenicol (0.25 mg/ml) as preservatives. The cells are then sensitised with IgG