DEL phenotype

Abstract

DEL red blood cells (RBCs) type as D– by routine serologic methods and are transfused routinely, without being identified as expressing a very weak D antigen, to D– recipients. DEL RBCs are detected only by adsorption and elution of anti-D or by molecular methods. Most DEL phenotypes have been reported in population studies conducted in East Asia, although DEL phenotypes have been detected also among Caucasian individuals. Approximately 98 percent of DEL phenotypes in East Asians are associated with the RHD*DEL1 or RHD*01EL.01 allele. The prevalence of DEL phenotypes has been reported among D– Han Chinese (30%), Japanese (28%), and Korean (17%) populations. The prevalence of DEL phenotypes is significantly lower among D– Caucasian populations (0.1%). Among the 3–5 percent of African individuals who are D–, there are no reports of the DEL phenotype. Case reports from East Asia indicate that transfusion of DEL RBCs to D– recipients has been associated with D alloimmunization. East Asian immigrants constitute 2.1 percent of the 318.9 million persons residing in the United States, and an estimated 2.8 percent are blood donors. Using these statistics, we estimate that 68–683 units of DEL RBCs from donors of East Asian ancestry are transfused as D– annually in the United States. Given the reports from East Asia of D alloimmunization attributed to transfusion of DEL RBCs, one would expect an occasional report of D alloimmunization in the United States following transfusion of DEL RBCs to a D– recipient. If such cases do occur, the most likely reason that they are not detected is the absence of active post-transfusion monitoring for formation of anti-D. Immunohematology 2017;33:125–132.

DEL in China: the D antigen among serologic RhD-negative individuals

“…They should be considered RhD-positive for several clinically relevant applications [ 9 – 12 ]. DEL has been reviewed before [ 3 , 13 – 15 ], albeit not with specific focus on East Asian populations.…”

“…Among 1,266 individuals with molecular data including PCR-SSP (polymerase chain reaction with sequence specific priming) or nucleotide sequencing or both for molecular signals of the RHD gene (Table 4 ), 96.7% were found to carry one distinct variant of the RHD gene, designated “Asian type” DEL [ 49 ]. The Asian type DEL is also known as RHD*DEL1 and RHD:c.1227G > A allele [ 15 ]. It had originally been described as RHD (K409K) in 2001 [ 9 ].…”

The <i>RHD</i> variants in Chinese population

“…However, carriers of DEL can still be D-negative donors, since there are fewer than 22 membrane RhD antigens per DEL RBC, as compared with thousands of RhD antigens on a normal RhD-positive RBC [23] . Unfortunately, allo-immunization following transfusion of DEL blood by D-negative recipients has been reported [25][26][27] . Therefore, more researches and clinical data accumulation are needed to clarify DEL serological characteristics.…”

RhD alloimmunization by DEL variant missed in donor testing

“…More than 40 DEL alleles have been described so far. 8,9 Generally, the frequency of DEL among Europeans is 1:350 to 1:2000 which is much lower than in Asian countries. 10,11 It has been well known that Rh antigens are highly immunogenic, with D antigen being most potent, followed by c, E, C,e.…”

“…Routine serologic testing cannot detect these variants and are therefore mistyped as D negative. More than 40 DEL alleles have been described so far 8,9 . Generally, the frequency of DEL among Europeans is 1:350 to 1:2000 which is much lower than in Asian countries 10,11 .…”