Repeat Testing for Weak D in Females of Childbearing Age?

Currently a transfusion service requires subsequent weak D (Du) testing of females of childbearing age on each admission - whether for prenatal testing or not. Based on AABB Standards and recommendations, the transfusion service in question does not think there is a specific requirement for "retesting" for weak D on subsequent admissions/specimens, but wants to know if there a general consensus about doing this? This transfusion service would like to only test for Du the first time the patient is tested. Would this meet AABB Standards? Is this considered "good practice"?

The following ideas have been submitted in response to the posed question. These opinions are paraphrased and are being presented without attribution. They do not represent an official opinion or position of the CBBS.

According to AABB standards (I4.200) "Rh type shall be determined with anti-D reagent. The test for weak D is unnecessary when testing the recipient". Therefore, we are never obliged to test for weak D. By not doing so, the only risk that we run is categorizing more individuals than are necessary as Rh negative (i.e. we haven't picked out those rare individuals who have weak expression of the D antigen. (Note: this is becoming an increasingly rare event as the sophistication of anti-D reagents makes it more likely to get reactivity without resorting to an antiglobulin reagent). By not testing for weak D, there will be some unnecessary transfusion of Rh negative units and administration of Rh immune globulin to weak D expressors (i.e. Rh positive individuals). So, do we need to repeat Du testing once we have determined that a patient is Du positive?

From the scientific and regulatory standpoint, it isn't necessary.

From a practical standpoint, however, it probably is. Once we type someone as Du positive (Rh positive), if we also don't do the same testing on subsequent admissions then we might risk a discrepancy in records (i.e. first determination: Rh positive; second determination: Rh negative). If this doesn't become confusing to staff, patients, clinicians or computer systems, then it might be a reasonable way to abridge testing and save a few dollars. Again, however, the relative infrequency with which most labs will need to do Du testing argues for being consistent from one determination to the next.

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