Policy Regarding Rh Blood Typing Tests

Effective: 3-29-02

The UMHS Blood Bank and Transfusion Service announces a new policy regarding Rh typing of prospective transfusion recipients and prenatal patients.

Policy Change: A test for weak expression of the Rh antigen D will no longer be performed on prospective transfusion recipients and prenatal patients.

Impact: This change may result in conflicts between past and current reports of a patient's Rh bood type. When this occurs, we will notify you via PathNet/Care Web of the change in our interpretation of your patient's Rh status. This notification will include, when relevant, any recommendations for change to the clinical management of your patient. Background: A patient's Rh status is determined by the presence or absence of red cell agglutination in direct tests with anti-D. Problems occur when the expression of D antigen is weak. Detection of weakly expressed D antigens requires the use of the indirect antiglobulin (Coombs) test. In the past, patients whose red cells typed as weak D (formerly called Du) were considered to be Rh-positive for the purpose of blood transfusion and RhIG prophylaxis. We now recommend that weak D patients receive Rh-negative blood and, if pregnant, are candidates for RhIG.

Rationale: This policy change is based on the following: 1) Some weak D phenotypes are the result of partial expression of D. 2) Patients of a partial D phenotype can make antibody to the parts of D that are absent from their red cells. 3) Changes have occurred in the formulation of RhD typing reagents. Studies indicate that current anti-D reagents will react directly with most weak D red cells that carry low numbers of normal D antigen. In contrast, many partial D phenotypes fail to react directly with current anti-D reagents.

If you have any questions or concerns regarding this notice, please do not hesitate to contact me at 763.6931, or one of the blood bank technical staff at 936.6888. W. John Judd, FIBMS, MIBiol Professor of Immunohematology May, 2002