Trinity Health - Ann Arbor Ypsilanti, Michigan, United States
Background/Case Studies: The US Preventative Services Taskforce (USPTF) guidelines recommend a type and screen (T&S) for all pregnancies at initial presentation and a repeat antibody screen on all RhD- women prior to 28 week prophylactic Rh immune globulin injection (RhIG). Our institution’s practice includes a first trimester T&S, with high inter-physician variability in the ordering of a repeat T&S prior to the 28 week RhIG injection. Due to the variations between local practice and USPTF guidelines, a retrospective analysis was performed to investigate cases of new alloantibodies identified at delivery. The goal was to better understand the clinical impact of the current practice and provide data to clinicians to help inform practice change.
Study
Design/Methods: The laboratory information system (LIS) was queried for all patients with a positive antibody screen associated with an ICD10 code for delivery. Data was pulled from mid July 2022 through early February 2024. Data included MRN, delivery date, first trimester T&S and antibody ID results, and pre-delivery T&S and antibody ID results. As a new LIS was implemented in July of 2022, the prior LIS was searched for the presence of any known antibody history.
Results/Findings: Eleven patients had a new clinically significant alloantibody at delivery. All 11 were RhD+, had a negative first trimester antibody screen and no prior antibody history, and none had a T&S at 28 weeks. See Table 1. Twenty-three patients presented with a new antibody of indeterminate specificity, including possible autoantibodies, antibodies to reagent diluent, low-frequency antigens, or non-specific reactivity. Passive anti-D from RhIG was identified in 538 patients. One patient had an anti-C, but it was known and monitored at a different system. One patient had anti-D at delivery, but no prior hospital records. Conclusions: In the data set, all new clinically significant antibodies identified at delivery were in RhD+ patients. No new anti-D antibodies were detected, suggesting the current RhIG prophylaxis protocol is effective. Of these patients, 10 would have required titer monitoring. Accessible crossmatch compatible units were delayed for all patients with new antibodies, including indeterminate specificity antibodies. Knowledge of this reactivity prior to delivery may improve availability of compatible blood, especially for scheduled C-sections. While the USPTF only recommends screening RhD- mothers at 28 weeks, the British Blood Transfusion Society recommends that all obstetrical patients, regardless of Rh type, should be rescreened at 28 weeks. The cost-benefit of this practice is questioned; however, our data suggests that routine monitoring of RhD+ patients may be clinically impactful. Institutions that adopt a universal 28 week T&S into their protocol can better identify and manage patients at risk of HDFN, and ensure they have compatible blood for when delivery is imminent.
