[can wash change the strength of the reaction]

The sample is cord blood.  Cord blood sample has to be washed several times before making cell suspension.  After the cell suspension is made, can you use one drop of that blood to perform DAT without any further washing?  The washing before making the cell suspension is sufficient? 

[can wash change the strength of the reaction]

Another tech performed the test and I tried to use this as a part of competency. 

We use the same saline for cell washer and manual washing.  I am not sure about the pH of the saline.  It is not PBS. 

[can wash change the strength of the reaction]

I performed a DAT with IgG on a cord blood sample.  I washed the cells about 4 times before making 3-5% cell suspension.  I washed that one drop of cells 4 times before adding IgG for DAT.  The DAT result was negative. 

I tried again.  This time, I put two drops of unwashed cells into a tube and washed the two drops of cells 4 times before I added IgG. This time the result was M+. 

What caused the differences?  Do you think the washing itself can change the result? 

 

Thanks.