How can you make Coomb's control cells in indirect anti-globulin test?

Preparing Coombs control cells is very easy. To about 10 drops of washed O Positive red cells add 5-6 drops of anti-D antisera. Incubate at 37C for 15 minutes. Wash 4 times then prepare a 3 to 5% cell suspension. To verify reaction, add two drops of AHG into test tube and one drop of newly prepared Coombs cells. Centrifuge on High for 15 seconds,,,should get 1 -2 + reaction.