Screening for c in D negative units

[cbaldwin]

I am posting this in the Education forum because I am a student. In the thread, "Topics for Education", numerous suggestions were offered, and I have a question about one of the suggestions. I am starting a new thread because it is a new subject.

“plus understanding the risks of making anti-c and why you don't screen the O negs for c when you have gone through all the O pos units”

I would like to make sure I understand this one. Anti-c is clinically the most important Rh antibody after D.

First, I'm assuming this is an emergency and the O positive units were given without screening, so the patient has been exposed to c. Secondly, the incidence of the c antigen in Caucasians is 80%, in Blacks 96% and in Asians 47%, so there is a good chance that if the patient is Caucasian or Black they won't develop anti-c.

I hope someone will correct me or comment on my musings. I am adsorbing a lot of information (such as the difference between adsorbtion and absorbtion) but information is not knowledge and I need all the help I can get!

Thank you!

[L106]

Hi Catherine. I'm not sure is you actually have a question, so my comments may be off-base.

There are some transfusion services that do screen Rh Positive donor red cells for the c antigen, but most facitilites do not screen for the c antigen. I think most facilities feel that it is not cost-effective to spend the time and reagent expense of doing the additional testing in order to prevent a patient from possibly producing Anti-c.

And since the vast majority of Rh Negative donor units are r/r (dce/dce, and therefore c Positive), it is definitely a waste of time & reagents to screen Rh Negative donor units for the c antigen.

I would not make your comment that "there is a good chance that if the patient is Caucasian or Black they won't develop Anti-c." We see several examples of Anti-c each year, and our population is almost exclusively Caucasian and Black. Also, since only 5-10 % of the population have unexpected antibodies, one could make the statement that "there is a good chance that the patient won't develop any unexpected antibodies, regardless of what their race is."

[cbaldwin]

Thanks L106--I think the information I was looking for is that the vast majority of Rh negative units are r,r (dce/dce)--C

[Mabel Adams]

Bingo. I'm pretty sure that was the intended point of the post you quoted. I am always trying to teach my staff that valuable little truism--almost all Rh neg blood is cde/cde. That fact then tells you not bother to screen them looking for units neg for c or e. It also tells you how to be almost sure you will find a compatible unit for someone with anti-E or C in an emergency or if you are just lazy and don't want to screen a bunch of units (the Rh neg unit should be a short-date, of course ) It also explains why our policy to test the patient that has made anti-E for the c antigen applies only to Rh pos patients. See, very useful little fact.

[Eagle Eye]

It also tells you how to be almost sure you will find a compatible unit for someone with anti-E or C in an emergency or if you are just lazy and don't want to screen a bunch of units (the Rh neg unit should be a short-date, of course )

And we need to keep eye on who is using RH Neg(O Negs) for patients who needs only C- or E-???

[Mabel Adams]

I saw a patient with anti-E come into ER once and take unxm blood. The tech did not look at his antibody history but was able to get him type-specific AB+ blood. I arrived at work just as she read his xm (1980's so full AHG xm on everyone and no computer to help check history) and looked panic stricken that the unit she had issued was incompatible. If she had read his antibody history she could have issued A neg blood and been pretty sure the uncrossmatched unit would be compatible. The patient died of the massive heart attack he was having before the unit was barely more than started but I have never forgotten that lesson.