Some background, we have an Ortho Vision.  We are validating the Poly IgG/C3d (DAT) card (when positive, it reflexes an IgG only DAT test).  I am attempting to use Hemo Bioscience C3 control cells to validate this card.  The cells do react appropriately (3+) in the poly card.  However, when the reflex tests runs the IgG card is also positive (weak to 1+).  Anybody know why these cells are reacting in the IgG only card?

I also see this on an occasional CAP survey.  I can only assume that it is due to the Compl on these cells.  Must have a small amount of agglutination/aggregation that the sensitivity of the  gel detects.

Cells are coated with complement artificially.  some methods will also cause IgG to be coated.  IF the cells are used according to the method they were designed for the manufacturer will have made sure that , in that method, the IgG does not react.  The problem starts when the complement-coated cells are used in other methods or, worse, for the CAP survey.  The C3-coated cells that are used for the CAP survey almost always react with anti-IgG in gel because of this - but the cells used are actually designed only to be used with anti-C3 in tubes.

so my advice would be, if you are using complement coated cells to control your anti-complement reagents, don't use them to check for negative reactions in anti-IgG