Clinical and Laboratory Update on the DEL Variant

Pornlada Nuchnoi, PhD; Jairak Thongbus, MSc; Apapan Srisarin, MSc; Usanee Kerdpin, PhD; Virapong Prachayasittikul, PhD


Lab Med. 2014;45(4):285-289. 

In This Article

Abstract and Introduction


Serological assays for the RhD blood group are based on detection of the RhD antigen on human red blood cells using a specific anti-D antibody. The weak expression of the RhD antigen in the DEL variant hinders the sensitivity of conventional serological assays. Evidence of anti-D immunization in patients with D-negativity who have received DEL-variant blood units has been reported in various populations. This observation has prompted the need for genetic epidemiological and clinical data on the DEL variant in the development of DEL molecular diagnostic testing. This review highlights the molecular features of the DEL variant, the clinical consequences of DEL-blood transfusion, and current approaches for detection of the DEL-variant for donor screening and transfusion.


Since the discovery of the Rh blood group system in 1940, RhD has been considered the most highly polymorphic blood group.[1] In addition to the RhD-positive (Rh+) and RhD-negative (Rh-) phenotypes, qualitative (partial D) and quantitative (weak D and DEL) variants have become increasingly important in the practice of transfusion medicine. The weak expression of RhD antigen, termed DEL or D elute (Del), was first reported in 1984.[2] DEL is the RhD blood group variant most commonly reported in the Asian population, particularly in individuals of Japanese and Chinese ethnicity. The prevalence of DEL variant is approximately 30% in Asian RhD-negative donors and 0.1% in white RhD-negative donors. The DEL variant is phenotypically similar to the RhD-negative phenotype and is routinely identified as RhD negative by conventional serological tests. The number of D-antigen sites per DEL red blood cell (RBC) is estimated to be less than 22 compared with the 30,000 antigen sites for normal D and 1500 to 7000 sites for weak D.[3–5] Consequently, the DEL variant is nonreactive in the antihuman globulin (AHG) test; this is different from the conventional weak D variant, which produces a positive screening result. Therefore, DEL variant is only detected by the adsorption-elution test (Figure 1).[6] The majority of current DEL research has focused on identifying the associations between the identification of DEL-associated alleles and alloimmunization in various populations. This review provides an update of the clinical considerations associated with the DEL variant.

Figure 1.

Characteristics of the DEL variant