John, I think we are seeing a change for Transfusion Services to NOT report patients with weakly reacting D's (we include those that react less than 2+ on I.S.) as Rh Positive. We now consider these patients as Rh Negative for Transfusion and Rh Immune Globulin candidates. We report them as Rh *Negative* with the comment described in the last paragraph below. (In our computer system, we use DEP (for dependent on reagents, testing, etc., but that doesn't report on the patient's chart). Our computer QA is set up so that DEP patients must receive Rh Negative blood (except for Autologous which would be Rh Pos). The following paragraphs are what we sent out to inform our clients about the change.
Connie Westhoff has two excellent reviews on this subject. I can't remember the exact issues, but she published a review of the Rh system in Transfusion in mid 2005 and another article in I think the latest issue of Immunohematology.
On October 24, 2005 the Transfusion Service discontinued weak D (Du) typing except for testing ordered on neonates and prospective fathers. This includes OB patients tested for physician offices.
American Association of Blood Banks Standards used to require weak D testing for OB patients; now it’s not even recommended. As molecular studies have progressed in the Rh system, it’s becoming clear that there are a significant number of patients who lack a portion of the D antigen and may become sensitized to parts of the D antigen. This is more apt to occur in patients who type weakly or variably with different Anti-D reagents, particularly as all Anti-D reagents are now at least partly monoclonal.
Many patients who in the past typed as weak D or Du positive with polyclonal reagents now type as D Positive with direct techniques using monoclonal reagents. So the remaining patients who type as weak D positive with current reagents are more likely to be missing part of the D antigen than those who typed as weak D or Du positive with polyclonal reagents.
This change will cause some confusion because patients who have previously been reported as Rh Positive Weak D (or Du) Positive will be considered as Rh Negative for transfusion and Rh Immune Globulin administration but will be considered as Rh Positive as blood donors.
When this change takes effect, patients whose red cells react variably with Anti-D reagent or those who were previously reported to be Weak D or Du Positive with monoclonal reagents will be reported as Rh *Negative* with the comment *Rh type is dependent on reagents used, tests performed, and/or technical performance. Patient may have been previously reported as Rh Positive or Rh Negative. For Transfusion Service testing, the patient will be treated as Rh Negative and will receive Rh Negative blood for transfusion and/or Rh Immune Globulin. As a Blood Donor, patient will be treated as Rh Positive.*:
Belva Sipherd
Except for neonates and prospective fathers, we report patients who type as Neg to 1+ with Anti-D on Immediate Spin as Rh Negative. (Exception: Patients known to be Rh Pos who receive many units of Rh Neg blood.) If an OB patient has previously been typed as weak D positive, we skip the Fetal Screen and go right to a K-B to determine fetal bleed. If we haven't previously typed the patient for weak D and the fetal screen is as strong as the positive control, we do both a K-B and a weak D test. If the patient is weak D positive, then for any subsequent pregnancy, we'd go right to K-B as skip the Fetal Screen if we needed to test for fetal bleed (i.e. delivery of Rh Pos baby).