Warm Autoantibodies

Warm autoantibodies (WAA) are targeted against “self” antigens on the red cell surface, and react best at body temperatures (contrast to cold autoantibodies). Warm autoantibodies typically react against all RBCs (they are “panagglutinins“), though they may occasionally show some increased strength when certain Rh antigens are present).

Here are some of the biggest issues to remember for people with WAAs:


  • Rule out alloantibodies. This is really top priority for these patients. Most patients with WAAs can receive blood from random ABO/RhD-compatible donors without a major problem, even though the crossmatch will be incompatible (that is not always true, though, so these patients should only be transfused when the clinical indication is clear). The blood bank’s main job, however, is to make sure that there are no other antibodies present in addition to the WAA. Specifically, since WAAs react against essentially all RBCs, it can be very difficult to identify antibodies against non-self RBC antigens. Such a workup may require special techniques like autoadsorption.
  • Choose appropriate blood. Once alloantibodies have been ruled out, blood banks have to choose the most appropriate blood product for the recipient with a WAA. According to a survey published in 2017 (Ziman A et al, Transfusion 2017;57:463-477), most centers recommend matching such donors for antigens that the patient lacks in the Rh and Kell blood group systems in order to prevent formation of new antibodies, but others recommend much more extensive matching. There is no consensus at this point.
  • Overlook the incompatible crossmatch results. Most often, all units crossmatched after steps 1 and 2 are done will be incompatible. Most blood banks will crossmatch multiple acceptable units and choose those that are “least incompatible” with the recipient serum/plasma (Please note that this method does not assure additional safety! Click for more on my most despised phrase in blood banking).
  • Explain things to the clinician. Many non-hematologist clinicians do not understand WAAs that well, so blood bankers often have to try to help them through the scary-sounding idea of transfusing blood with incompatible crossmatches! However, when you do so, please don’t try to reassure them by breaking out the “we chose the least incompatible units for your patient” argument! As mentioned above, while we often choose to give the unit that is most compatible on crossmatch, doing so in no way ensures more safety.

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