Today we will be discussing patients that have a weak D phenotype for their Rh blood group antigen. Since the introduction of Rh immunoprophylaxis to prevent maternal-fetal alloimmunization, rates of severe and fatal hemolytic disease of the fetus and newborn have dramatically declined. Although laboratory practices in the United States are not consistent, blood donors and newborns with a serologic weak D phenotype are often classified as RhD-positive, while pregnant females with this same phenotype are treated as RhD-negative to avoid alloimmunization.
An AABB and College of American Pathologists Work Group recently recommended that obstetric patients and transfusion recipients with some weak D alleles should be managed as RhD positive, since only certain RhD alleles are associated with any risk of alloimmunization.
Dr. Sandler explains:
“Approximately 0.2 to 1.0% of Caucasian women will have a serologic weak D phenotype detected by routine RHD typing. Depending on the race and ethnic group, as many as 95% of women with a serologic weak D phenotype will be determined to have an RHD genotype 1, 2 or 3 which could and should be managed as RhD positive.”
RHD genotyping in individuals with a serologic weak D phenotype may avert over 24,000 unnecessary injections of Rh immunoglobulin each year in the United States.
In a recent article in TRANSFUSION, researchers examined the financial implications of genotyping pregnant women with a weak D phenotype.
Dr. Vassallo summarizes their findings:
“We were able to construct a robust statistical model to evaluate the costs of common practice without RHD genotyping and use of Rh immunoglobin versus genotyping and management according to the presence or absence of weak D types 1, 2 or 3 and found that really over 10-20 years it was a 2-4 cent per pregnancy cost savings for a total $645,000 to 2 million dollars over that 10-20 year period.”
The analysis found the savings vary by ethnic group, but the overall savings occur when the assay is less than $256.
Dr. Delany summarizes:
“Red cell genotyping can really improve and make blood typing more precise. The financial analysis provides supporting evidence that not only does the technological advancement provide more precision for blood typing, it also won’t cost us more.”
We’ll be back with another edition of Transfusion News on September 30th. Thanks for joining us.
- Delaney M. What is the value of a blood type? Transfusion 2015;in press.
- Kacker S, Vassallo R, Keller MA, Westhoff CM, Frick KD, Sandler SG, Tobian AA. Financial implications of RHD genotyping of pregnant women with a serologic weak D phenotype. Transfusion 2015. DOI: 10.1111/trf.13074.
- Sandler SG, Flegel WA, Westhoff CM, Denomme GA, Delaney M, Keller MA, Johnson ST, Katz L, Queenan JT, Vassallo RR, Simon CD, College of American Pathologists Transfusion Medicine Resource Committee Work G. It’s time to phase in RHD genotyping for patients with a serologic weak D phenotype. College of American Pathologists Transfusion Medicine Resource Committee Work Group. Transfusion 2015;55: 680-9.