RHD genotyping to resolve weak and discrepant RhD patient phenotypes

Abstract

Background: We instituted RHD genotyping in our transfusion service for obstetrical patients and transfusion candidates. We sought to examine how RHD genotyping resolved weak or discrepant automated microplate direct agglutination (MDA) RhD phenotypings and impacted needs for Rh Immune Globulin (RhIG) and D-negative RBCs.Study Design and Methods: We investigated RhD phenotypes with equivocal or reagent-discrepant automated MDA (Immucor, Norcross, GA), weak-2+ immediate-spin tube typings, historically discrepant RhD typings, or D+ typings with anti-D. We performed microarray RHD genotyping (RHD BeadChip, Immucor BioArray Solutions, Warren, NJ). Patients were managed as D+ with weak-D types 1, 2, and 3, and as D-negative with all other results. Results: Our weak-D prevalence was 0.14%. Among 138 patients (73 obstetrics, 65 transfusion candidates), 38% had weak-D types 1, 2 or 3, 25% weak partial type 4.0, 21% other partial-D variant alleles, and 15% no variant detected. One novel allele with weak partial type 4.0 variants plus c.150T>C (Val50Val) was discovered. Weak D types 1, 2 or 3 were identified in 66% (48/73) of Whites versus 3% (2/62) of diverse ethnic patients (p < .0001). RHD genotyping changed RhD management in 60 patients (43%) (49 to D+, 11 to D-negative), resulting in net conservation of D-negative RBCs (98 avoided, 14 given) and RhIG (8 avoided, 3 given). Conclusion:In our patient population, equivocal or reagent-discrepant MDA RhD phenotypes were highly specific for weak-D or partial-D RHD genotypes.Resolution of RHD genotype status reduced our use of D-negative RBCs and RhIG.

RHD‐negative red cells may be avoided for patients with ambiguous serologic typing for the RHD antigen

“…0.28% of our patients had ambiguous results in serologic RHD‐testing, 0.26% of those due to an aberrant, weak or partial, RHD variant. This was higher than in another, recently published study, investigating an ethnic more diverse population with a prevalence of RHD variants of 0.14% 14 but lower than that reported for Denmark (0.6% and 0.7%), 15,16 a country directly neighboring the region where our patients are originating from. Reasons might be different study protocols, a different sensitivity in the assays, 17 and the experience of the investigators, who observed the test results.…”

Weak or discrepant RhD phenotypes: Laboratory management strategies for local patient populations

“…As kindly cited by Juhl et al, our group previously reported in TRANSFUSION our 2.5-year experience (2019-2021) with RHD genotyping for weak or discrepant patient RhD phenotypes in an American academic medical center serving a diverse urban community. 5 Our serological and RHD genotyping criteria and methods and our management of Rh immune globulin and D-negative transfusions were described. We also routinely performed Rh CcEe phenotypes by tube method (Gamma-clone, Immucor, Norcross, GA) in these patients.…”

“…We managed type 4.0 patients as D-negative for transfusion unless they had difficult antibodies or high blood needs. 5 Nine of 16 C+ patients (56%) with type 4.0 or other partial RHD variants expressed a partial C phenotype from the hybrid variant RHD*03N (RHDIIIa-CE(4-7)-D) (3N).…”

Estimating the serological underrecognition of patients with weak or partial RHD variants

“…Weak or discrepant RhD phenotypes occur in 0.1%–0.4% of US patients 1–5 . Rates vary greatly by race, for example, 0.1% of Whites and 0.6% of Blacks in our Chicago obstetrical service 1 .…”

“…Weak or discrepant RhD phenotypes occur in 0.1%–0.4% of US patients 1–5 . Rates vary greatly by race, for example, 0.1% of Whites and 0.6% of Blacks in our Chicago obstetrical service 1 . The definition of weak D phenotype has expanded from nonreactive by direct agglutination and antiglobulin reactive with IgG antisera to also include weak‐2+ direct agglutination reactions 6,7 .…”