Phasing-in RHD genotyping.

Abstract

In this issue, Sandler and colleagues 1 report the results of the College of American Pathologists (CAP) J-B Transfusion Medicine (Comprehensive) and Educational Survey, in which more than 3100 institutions describe how they perform Rh typing for blood donors, pregnant women, and hospital patients. In accordance with American Association of Blood Banks (AABB) Standards for Blood Banks and Transfusion Services, most hospital laboratories reported that they do not routinely perform a serologic weak-D test on pregnant women or transfusion recipients. This practice results in most pregnant women and hospital patients with a weak-D phenotype being categorized and managed as Rh (Table 1). In contrast, a weak-D test is performed routinely on blood donors whose red blood cells test D by direct agglutination, resulting in most blood donors with a weak D being categorized and managed as Rhþ.2 This 50year practice appears to be relatively safe, and there are only a few published reports of persons with a weak-D phenotype forming anti-D antibodies. However, this practice confuses patients, blood donors, and caregivers and uses Rh immune globulin (RhIG) and Rh red blood cells for many persons with a weak D, who could be safely managed as Rhþ, if their genotypes were known. The CAP Transfusion Medicine Resource Committee (TMRC) reviewed this practice in the context of the current state of science for RHD genotyping. The TMRC concluded that selective integration of RHD genotyping of weak D phenotypes could improve the accuracy of Rh typing results, thereby reducing unnecessary administration of RhIG in women with a weak D phenotype, and decrease transfusions of Rh red blood cells in recipients with a weak D phenotype. The process of phasing-in RHD genotyping in clinical practice has begun in many hospitals, but as the CAP survey indicates, most pregnant women and hospital patients in the United States continue to have their Rh type determined by dated serologic methods. Those laboratories that do not routinely perform weak-D tests for patients typing Rh by direct agglutination with anti-D should now begin to introduce Rh typing reagents and procedures selected to detect, not to avoid detection of, weak-D phenotypes.