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Background and Objectives: A high proportion of suspected weak D patients referred to Héma‐Québec were genotyped as weak D type 42 (368/2105, 17.5%). These patients are currently considered D with regard to RhD immunoprophylaxis in pregnancy and transfusion. The goal of this study was to retrospectively evaluate the risk of alloimmunization in weak D type 42 patients and to characterize their RhD surface molecule expression on red blood cells (RBCs) in comparison to other weak D types (1, 2 and 3). Materials and Methods: A retrospective analysis using the weak D type 42 patients' medical data to verify potential anti‐D alloimmunization events was conducted. Quantitative analyses using flow cytometry were also performed on RBCs to quantify the cell surface density of the D antigen. Results: Data on 215 subjects with weak D type 42 were reviewed. None developed immune allo‐anti‐D; three had definite exposure to D+ red cells and 41 had possible exposure through pregnancy. Flow cytometry analysis showed that weak D types 1, 2, 3 and 42 had relative antigen densities of 2.7%, 2.2%, 8.1% and 3.6%, respectively, with R1R2 red cells referencing 100% density. The estimated antigen density range of weak D type 42 was 819–1104 sites per RBC. Conclusion: Our retrospective alloimmunization data analysis and antigen density study establish a basis for the consideration of a weak D type 42 individual as D+. This consideration would allow for a targeted reduction of RhD immunoprophylaxis in pregnancy and the unjustified use of D– units for transfusion. [ABSTRACT FROM AUTHOR]

Background and Objectives Materials and Methods Results Conclusion Postpartum anaemia is a prevalent health problem. We aimed to determine the compliance rate for red blood cell (RBC) transfusion indication among postpartum women in a single tertiary care centre in Quebec, Canada.Retrospective cohort study including all women ≥6 h postpartum who received ≥1 RBC transfusion during their delivery hospitalization between January 2005 and February 2022. We determined our centre's compliance rate by indication as compared to current society guidelines, all published after 2015 (Network for the Advancement of Patient Blood Management, Haemostasis and Thrombosis [NATA], Royal College of Obstetricians and Gynaecologists [RCOG], American College of Obstetricians and Gynecologists [ACOG]). We then explored predictors of guideline non‐compliance and described transfusion practices in our centre.A total of 171 women were included. Our centre's compliance rate was 79.5% (95% confidence interval [CI] 72.7–84.8). Predictors of guideline non‐compliance were maternal medical comorbidity or abnormal placentation, both limited by large CIs (odds ratio [OR] 2.26, CI 1.02–4.94, p = 0.04; OR 4.00, CI 1.31–12.06, p = 0.01, respectively). Postpartum haemorrhage was diagnosed among 68% of the cohort, mostly due to uterine atony (73.3%). Mean baseline and nadir haemoglobin were 111 g/L (±18) and 62 g/L (±7.7), respectively. Multiple unit initial transfusion was found in a majority of patients (63.7%). Iron therapy was administered to 51.5% of women in‐hospital and 81.9% received an oral iron prescription at discharge. There were no differences in primary or secondary outcomes subsequent to relevant guideline publication.Our centre's compliance rate for RBC transfusion indication meets current practice guidelines. Areas for improvement include single‐unit initial transfusion protocols and adjuvant iron treatment. Antenatal optimization of haemoglobin and ferritin stores may limit postpartum transfusions. [ABSTRACT FROM AUTHOR]