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Passive Anti-C due to recent RhIG administration

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Do other hospitals have a policy for handling passive Anti-C?

It is published in the Rhophylac package insert that Anti-C may also be present along with the Anti-D.

I work at a hospital with a High Risk Maternity ward and we often have moms-to -be here as inpatients for weeks or months before the baby is delivered due to complications.

Here is what happens at our lab:  The mom gets RhIG  (we use Rhophylac) at 27 weeks, or any time the MD decides to give another dose due to complications, and then a few days later we are running a type and screen if they are at risk for going into premature labor due to their complications.

Well yes, we do detect the Anti-D, but when the RhIG has been administered within a month or less, we often see the Anti-C as well.  Especially on our ECHO.  We do not use gel, we have PeG as our alternate method.

Where I am going with this is I am looking for more info from other labs on about how far out from the last RhIG dose are you seeing this passive Anti-C?  In my experience, it is usually less than one month from the last RhIG dose.  After it has been more than about 30 days, we usually no longer detect the Anti-C, only the Anti-D.

I wanted more information in order to develop a policy for when we can call it Passive Anti-C and when we need to treat it as a potential alloantibody.  I was planning to make my cut-off date one month from the date of the most recent RhIG., and also the mom had to have had a negative antibody screen prior to the RhIG administration during the same pregnancy.

Any advice you might have would be welcome.

Probably the easiest thing would just be to run the panel with PeG and hope the Anti-C is not detected?


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I would think a month is entirely adequate.

Think about how the mother would have made an allo-anti-C, without making an allo-anti-D.

We presume, in these cases, that the mother is the classic rr (D-, C-, E-, c+, e+), and so can make anti-D, anti-C and anti-E of the common Rh antibodies (she cannot make either anti-c or anti-e).

For the mother to make an anti-C, but not an anti-D, when the mother has received a dose of prophylactic anti-D immunoglobulin, the baby/foetus has to express the C antigen, while not expressing the D antigen (ignoring anti-G for now).  This almost certainly means that the father and the foetus must have the RH*Ce gene, but not the RH*D gene; an unusual, but by no means rare, situation.  What would be rare, however, would be an individual who, having been given a dose of prophylactic anti-D immunoglobulin, which would, of course, "get rid of" foetal red cells expressing the D antigen (which is extremely immunogenic) but would still give her immune system time to be sensitised to the C antigen, when both the D and C antigens are expressed on the same red cells (if you see what I mean).  On top of that, the C antigen is known to be nowhere near as immunogenic as the D antigen, and the likelihood gets even lower.

Finally, look at the literature on anti-C causing HDFN.  It is incredibly rare for anti-C (or anti-Ce) to cause clinically significant HDFN, let alone fatal, HDFN, and you will see that the chances of your pregnant women having an anti-C that will cause HDFN, particularly when it is no longer detectable in the plasma, is not so much disappearingly low, as miraculous!

I really wouldn't worry about it.

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Thank you very much for your response. That is great information to report to the techs here.  Some of them are nervous about how we can differentiate passive Anti-C from allo anti-C.  And the answer is, of course, that we cannot, except by titer, and even that is not fool-proof unless the titer is very high.

 I did not clarify very well that the focus of my question is about how we are handling the record for the mother. I want to change our policy to manage these passive Anti-C examples the same as if it were passive Anti-D.

Our current situation is to report any antibody(ies) detected.  I want to create a system whereby we record the detection of a "passive Anti-C" and treat it the same as our Passive Anti-D.   I do not want to record in her antibody file record that she has "Anti-C" because our system is programed to treat this as an alloantibody and requires her to receive C negative blood with an AHG crossmatch.  When we have these high-risk moms staying on our ward for months, that can really add up to a lot of crossmatches and antigen typing bills, not to mention unnecessary use of resources.  We sometimes end up recrossmatching the same antigen negative units every 4 days for the same patient while she is here for several weeks.

Our LIS can handle another code for passive Anti-C, and that is my goal to create that code.  But I want to also make very strict rules about when that code can be used, based on our experience and any feedback I can get from other laboratories.

For example, the code can only be used when the mom has had RhIG within the last 30 days and no previous antibodies other than Passive Anti-D.

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