Red blood cells (RBCs) from Asian-type DEL blood group express very weak RhD antigen and are falsely typed as RhD-negative blood group in routine RhD testing. Until now, Asian-type DEL (D-eluate) patients still be treated as rare RhD-negative patients in the clinic. Previous study from the Asian-type DEL pregnant women with RhD+ fetus showed no occurrence of alloanti-D immunization. This result, however, does not directly be applied for Asian-type DEL patients receiving RhD+ blood transfusions, as lacking of direct evidence regarding the safety and underlying mechanism.

In this study, the patients with Asian-type DEL were identified and received RhD+ blood transfusion, then evaluations of any adverse reactions, especially the active follow-up alloantibody test, were prospectively conducted.

Red blood cells (RBCs) from Asian-type DEL individuals express very weak RhD antigen and are falsely typed as RhD-negative in routine RhD testing. Recent studies have shown that 9-30% of individuals with a serologically apparent RhD-negative phenotype in East and Southeast Asian populations, including Chinese, Korean, Japanese, Thai and Myanmar, actually are not truly RhD-negative but exhibit the DEL (D-eluate) phenotype, which represents almost 1.7 million Asian-type DEL individuals in China, 250,000 in Korea, Japan, Thailand, and Myanmar as well as at least 90,000 in the US among Asian immigrants. Nowadays, Asian-type DEL patients are conventionally transfused with RhD-negative RBC, which are difficult to organize because of the undersupply of the rare RhD-negative blood in these Asian countries, due to low frequency distribution (0.3-0.4%).

However, our previous study demonstrated that Asian-type DEL pregnant women with RhD+ fetus did not develop alloanti-D during the pregnancy. Latter, this phenomenon was confirmed by different medical centers in China. Accordingly, Asian-type DEL patients may also not be able to produce alloanti-D after transfusion with RhD+ RBC and consequently the use of RhD-negative RBCs for the transfusion management of Asian-type patients may be superfluous. However, this hypothesis needs to be carefully proved.

In this study, we were able to verify this assumption. Blood samples from 2,011 Chinese patients with a primary RhD-negative phenotype from the hospitals in Guangzhou of China were typed for Asian-type DEL blood group in the Guangzhou Blood Center. DEL phenotyping was performed by the serological adsorption/elution antibody testing and genotyping for the Asian-type DEL specific allele (RHD*1227A) detection was conducted using a well validated high-resolution melting (HRM) approach. Then, transfusions of RhD+ RBC were performed in a cohort of Asian-type DEL patients. After RhD+ blood transfusion, evaluations of any adverse reactions, especially the active follow-up alloantibody test, were conducted to evaluate the alloanti-D immunization. Besides, effectiveness of transfusion (Hb changes) was also recorded.

Inclusion criteria for eligible participants were as follows: (1) Asian-type DEL blood group; (2) male patients, or female patients ≥ 49 years of age, or female with severe illness and no plan for further pregnancy; (3) needing blood transfusion in line with guidelines for internal medicine or surgery; and (4) signed voluntary informed consent for blood transfusion treatment before the trial.

The exclusion criteria were: (1) adverse reaction in a previous transfusion; (2) allergies to blood products or immunodeficiency diseases; (3) needing massive blood transfusion for acute blood loss; (4) positive pregnancy test results; (5) conscious dysfunction or severe mental illness; and (6) unsuitability for the study, as estimated by the principal investigators.

Eligible participant inclusions were as follows: (1) all male Asian-type DEL patients; (2) female Asian-type DEL patients beyond the gestational age (≥49 years); (3) female Asian-type DEL patients of childbearing age but with severe illness and no plan of further pregnancy

Assessed up to 1354 days following transfusion, a median of 226 days

In the condition of correct blood group typing and cross-matching before transfusion, and carefully checking and monitoring during the transfusion, the transfusion treatment is quite safe with very low frequency of serious adverse event and mortality.

A large-scale clinical trial cannot be conducted since Asian-type DEL is rarely distributed in our population, with a frequency of approximately 0.1%. Additionally, a prudent inclusion criterion was adopted in this study to avoid potential alloanti-D immunization and negative influences on pregnancy in women of reproductive age and young girls, in which they were excluded from the trial with great caution.