Background/Case Studies: Newborn cord blood testing is routinely performed on neonates of Rh(D) negative mothers for purposes of Rh Immune globulin administration. A recent change by our obstetrics practice requires testing of all cord bloods from mothers who are ABO group O. Cord blood testing includes an ABO/Rh and DAT (Direct Antiglobulin Test). When the cord blood ABO/Rh cannot be resolved because of potential maternal contamination, a redraw of EDTA venous blood via a heel stick is requested to verify the newborn’s ABO/Rh. The goal of our study was to determine the value of the redraw for resolving the discrepancies and to eliminate the redraw sample, if warranted.
Study
Design/Methods: Data was collected on cord blood samples from newborns that were tested for an ABO/Rh and poly-specific DAT. All samples were evaluated for cases in which the ABO/Rh was tested and found to have a mixed field appearance in the forward typing when tested in gel using OrthoMTS™ Gel Cards, and then subsequently confirmed in tube testing. A heel stick ABO/Rh sample was collected to determine if the mixed field was due to potential maternal contamination in the cord blood or weakened antigen expression in the newborn. The mixed field caused by maternal contamination was expected to resolve in the heel stick sample (redraw).
Results/Findings: In 2023, 13 of 137 cord blood samples received in our Immunohematology Reference Laboratory (IRL) required venous redraws due to an ABO/Rh discrepancy, including 10 from group O mothers (9 O pos, 1 O neg). Of the 10 redraws from group O samples, 6 showed no mixed field and resolved the ABO/Rh. Conversely, mixed field reactivity remained in 4 redraws, most likely from the newborn’s weakened antigen expression due to the gestational age (GA) at the time of birth. Conclusions: A heel stick/redraw sample resolved 60% of ABO/Rh typing discrepancies detected in newborn cord blood samples. Rather than automatically reflex an additional collection, which is both time consuming and painful for the patient, the IRL will request the patient’s physician evaluate the clinical need of a valid ABO/Rh type for newborns of Rh(D) positive mothers by resulting the discrepant ABO/Rh with a comment stating the newborn’s blood type cannot be interpreted due to possible interference from mother’s blood in the cord blood sample. Newborns of Rh(D) negative mothers, however, will continue to be redrawn to determine Rh immune globulin needs for the mother.
