(P-IG-46) Weak and Partial D Genotype Frequencies in a Large Integrated Healthcare Delivery System in the USA

The D antigen is one of the most immunogenic blood group antigens and includes partial D and weak D types.  There is limited information on the prevalence of D variants among diverse populations. A survey of over 3100 labs performed in 2014 confirmed that inconsistent policies and procedures for RhD testing existed nationwide.  These assorted procedures mean different rates of RhD variant detection, which leads to varied prevalence data in the literature. 

Study

Design/Methods:

All patient samples submitted for ABO RH typing to a large integrated healthcare delivery system Regional Reference Lab during a 40-month timeframe were screened for the presence of a potential D variant using a dual platform workflow.  First samples were run on a solid phase (Immucor NEO) analyzer and compared to historical results.  Patients without a historical type, with a discrepant historical type or indeterminate result by NEO were then passed to gel (ORTHO VISION).  If the gel showed discrepant results from the solid phase, the specimen was sent out for weak or partial D genotyping to an outside reference lab that used multiplex sequence specific primer (SSP) PCR to detect the most common weak D and partial D alleles. Race/ethnicities were pulled from the electronic medical record and are designated by the patient.

Results/Findings:

Over the 40-month timeframe, 715 patients were identified as potential RhD variants when historical results did not match current or when different methodologies showed discrepant results (e.g. gel and solid phase, or gel and tube testing did not match.). In total 34 RhD alleles were identified (able 1). Type 4.0 was the most common allele identified (n=160).  There were 80 patients whose genotype could not be identified by the alleles covered in the PCR assay.  The majority of genotyping cases were performed for pregnant patients. Of the 715 patients, almost half (346) had weak or partial D results that could be managed as RhD positive, highlighting the importance of incorporating RhD genotyping into the workflow to help avoid unnecessary administration of RhIG and preserve O negative inventory.   

Conclusions: The regional lab dual platform workflow identifies potential RhD variants that would be unrecognized using a single platform.   Over 10% of all patients sent for genotyping did not have a detectable common varient.  The majority (60%) of our self-identified Asian patients had no common variant detected.  Our self-identified Hispanic, Black/African American, and white populations also had a significant proportion of patients with no common variant detected (26%, 18% and 10%, respectively).   We show which populations have the highest proportion of variants unidentified by a SSP PCR assay covering the most common Weak and Partial D genotypes. Our data highlight the need to consider tailoring sequencing strategies for a diverse population

Importance of research: We present weak/partial D data that is from a geographically large and ethnically divers population, obtained using a unique dual platform workflow.