Diagnosis:
Immunohemtology: Pretransfusion testing, check cells
• Check cells are red cells that are coated with IgG antibodies. They are added to verify negative results obtained at the anti-human globulin stage.
• Causes of false-negative results with check cells include inadequate cell washing, delay in adding the anti-human globulin reagent following washing, and failure to add the anti-human globulin.
• Inadequate washing may lead to false-negative results with check cells because inadequate washing can leave free plasma antibodies behind. Anti-human globulin preferentially binds to free antibodies in solution rather than antibodies on red cells. Thus, if there are free antibodies left over as a result of inadequate washing, this will block function of the anti-human globulin reagent, preventing agglutination.
• If there is significant delay in adding the anti-human globulin reagent, IgG antibodies can fall off from sensitized red cells incubated in saline. Thus, these free IgG antibodies can block function of the anti-human globulin reagent, preventing agglutination.
• Check cells are not required in all testing methods. For example, gel testing systems do not use check cells. Each manufacturer will specify controls that must be used with a specific method.
