(P-IV-7) Preserving Rh-negative RBC Inventory: Safety of Transfusing Rh-positive RBCs to Selected Rh-negative Patients

Background/Case Studies: Rh-negative red blood cells (RBCs) are sometimes hard to procure. Maintaining an adequate inventory of Rh-negative RBCs is essential as these units are used in emergency situations when patient’s blood type is unknown, neonatal transfusions, transfusing Rh-negative females of childbearing age, patients alloimmunized to the D antigen, among other situations. This review aims to look at the safety of transfusing Rh-positive RBCs to eligible Rh-negative, a strategy our blood banks have implemented to spare Rh-negative inventory.

Study

Design/Methods: At our institution, blood banks aim to maintain an adequate stock of Rh-negative RBCs. When inventory falls below a defined par level, technologists are instructed to implement “Rh switching,” in which O positive RBCs are transfused to select Rh-negative patients. According to our protocol, this includes Rh-negative male patients over 18 years of age and Rh-negative female patients over 55 years of age. A retrospective review was conducted to evaluate immunohematologic outcomes in Rh-negative patients who received at least one Rh-positive RBC between January 2022 through December 2024. Relevant data collected included ABO/Rh blood group, number of RBC units transfused, presence of alloantibodies, and any transfusion reactions.

Results/Findings: This review included 350 Rh-negative patients who received a total of 1,699 Rh-positive RBC units (range: 1–73 units; median: 3 units). Of these, 279 (79.7%) patients were blood group O and received a total of 1,319 Group O positive RBC units. Long-term follow-up antibody screens (≥21 days post-transfusion) were not available for 191 patients. Among them, 65 patients died following the transfusion, and 126 were lost to follow-up. A total of 33 patients (9.4%) developed anti-D antibodies, with a median follow-up period of 83 days (range: 10–317 days). The median age of alloimmunized patients was 69 years (range: 26–97), and 17 (51.5%) were male. These patients received a median of 6 Rh-positive RBC units (range: 1–30 units) prior to developing anti-D. No transfusion reactions or delayed hemolytic transfusion reactions were observed.

Conclusions: Transfusing selected RhD-negative patients with RhD-positive RBCs is a low-risk strategy that supports the conservation of RhD-negative RBC inventory. The observed alloimmunization rate of 9.4% in this review aligns with previously published studies. While alloimmunization remains a recognized risk, it is considered an acceptable trade-off in carefully selected patient populations to preserve this critical and limited blood resource.