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Risk of RhD Sensitization

A prospective single-center observational study was undertaken at the University Medicine Greifswald between Jan 1, 2001, and Dec 31, 2015 to determine the risk of Rh D sensitization in RhD negative patients who were transfused with Rh positive red blood cell units. Two patient populations were analyzed; emergency patients with unknown blood type and RhD negative patients receiving RhD positive red blood cell units because of shortages of RhD negative red blood cells.

The primary endpoint of this study was anti-D alloimmunisation at 2 months follow-up or later. Patients were tested for immunisation against red blood cell antigens using the direct antiglobulin test and an antibody screen every 3 to 5 days for 4 weeks or until death, or hospital discharge. Surviving patients were screened for development of anti-D antibodies for up to 12 months after RhD positive red blood cell transfusion.

A total of 437 emergency patients, of whom 85 (20%) were RhD negative, were transfused with 2836 RhD positive red blood cell units. Seventeen or 4% of these 437 patients developed anti-D antibodies. During this same period, 110 known RhD negative patients were transfused with RhD positive red blood cell concentrates because RhD negative units were not available. Twenty nine of these 110 patients (26%) developed anti-D alloantibodies, which was significantly higher than the emergency patients with unknown blood type.

In general, only 7 percent of the population has an O Rh negative blood type. While only 6 to 7% of the general population is O Rh negative, approximately 12% of all RBC units issued are O Rh negative. Maintaining this level of O Rh-negative red cell inventory is becoming increasingly more difficult as the population ages and blood collections decline.

Transfusion of O Rh negative red cells to patients of other groups and types is occasionally necessary to protect females that may go on to have pregnancies. Using O Rh negative red cells for other transfusion recipients places an added strain on the blood supply and on the O negative donors who help support it. This reduces the availability of O negative units for recipients who should or must receive only this type.

According to this study, transfusing emergency patients with unknown blood type with O RhD positive red blood cells has a low risk of inducing anti-D antibodies (3–6%), but decreases the demand for O RhD negative red blood cell units by more than 10%. Widespread acceptance of this practice would decrease shortages of O RhD negative red blood cell units and insure their availability for Rh negative females of childbearing age and patients who are already sensitized with anti-D alloantibody.

Selleng K, Lancet Haematology, April 4, 2017



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