Background/Case Studies: New lessons are still being learned from a decade-old recommendation. In 2015, AABB and the College of American Pathology (CAP) released recommendations for incorporating RHD genotyping into weak D testing protocols for pregnant women and females of childbearing potential. The goal is to prevent RhD alloimmunizations, unneeded Rh immunoglobulin (RhIG) injections and unnecessary RhD negative blood transfusions. Parkview Health developed its genotyping algorithm a short time later (Figure A). Its blood banks use two anti-D reagents for automated and tube testing, allowing scientists to compare reactions between two antibody clones. Approximately 90% of Parkview’s genotyped patients are found to have RHD mutations. Of those, nearly 60% are ultimately treated as RhD negative.
In early 2025, two cases prompted Parkview to consider expanding its algorithm. Two patients had discrepant RhD types when compared to other health systems that use different testing methodologies. In both cases, Parkview phenotyped the patients as RhD negative. The other health systems typed them as RhD positive. At the time, Parkview’s algorithm did not address results that are discordant with those from other health systems. Blood bank leaders decided genotype results from both patients would help them determine if policy changes need to be made.
Study
Design/Methods: Collecting and retrieving a specimen from the first patient required collaboration. The patient had moved nearly 200 miles away from Parkview’s main campus. After she consented to the testing, Parkview coordinated the specimen collection and courier pickup with her current obstetrician. The second patient was a Parkview inpatient when scientists discovered the RhD discrepancy.
Parkview sends its genotype specimens to a molecular laboratory in Milwaukee for testing.
Results/Findings: The molecular laboratory determined the first patient has a Weak D Type 4.2.1/4.2.2 allele and recommended treating her as RhD negative. The testing on the second patient uncovered a Weak D Type 2 allele. The laboratory recommended treating this patient as RhD positive. Conclusions: Since Parkview phenotyped both patients as RhD negative, scientists did not suspect the women had RHD mutations. If genotyping had not been performed, the first patient would have been treated the same, regarding RhIG and transfusions. While the second patient would likely not have been harmed, she could have received unnecessary RhIG injections and RhD negative blood transfusions.
Blood bank leaders have concluded that even though Parkview’s reagents, methodologies and policies work well, it is important to consider other health systems’ results. Parkview has since expanded its algorithm to include “discordant with other health system’s typing” as a trigger for RHD genotyping.
